Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4992,31 +4992,32 @@
   if (Constant *C = simplifyFPOp({Op0, Op1}, FMF, Q, ExBehavior, Rounding))
     return C;
 
-  if (!isDefaultFPEnvironment(ExBehavior, Rounding))
-    return nullptr;
-
   // fsub X, +0 ==> X
-  if (match(Op1, m_PosZeroFP()))
-    return Op0;
+  if (ExBehavior == fp::ebIgnore || FMF.noNaNs())
+    if (match(Op1, m_PosZeroFP()))
+      return Op0;
 
   // fsub X, -0 ==> X, when we know X is not -0
-  if (match(Op1, m_NegZeroFP()) &&
-      (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
+  if (ExBehavior == fp::ebIgnore || FMF.noNaNs())
+    if (match(Op1, m_NegZeroFP()) &&
+        (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
     return Op0;
 
   // fsub -0.0, (fsub -0.0, X) ==> X
   // fsub -0.0, (fneg X) ==> X
   Value *X;
-  if (match(Op0, m_NegZeroFP()) &&
-      match(Op1, m_FNeg(m_Value(X))))
+  if (ExBehavior == fp::ebIgnore || FMF.noNaNs())
+    if (match(Op0, m_NegZeroFP()) &&
+        match(Op1, m_FNeg(m_Value(X))))
     return X;
 
   // fsub 0.0, (fsub 0.0, X) ==> X if signed zeros are ignored.
   // fsub 0.0, (fneg X) ==> X if signed zeros are ignored.
-  if (FMF.noSignedZeros() && match(Op0, m_AnyZeroFP()) &&
-      (match(Op1, m_FSub(m_AnyZeroFP(), m_Value(X))) ||
-       match(Op1, m_FNeg(m_Value(X)))))
-    return X;
+  if (ExBehavior == fp::ebIgnore || FMF.noNaNs())
+    if (FMF.noSignedZeros() && match(Op0, m_AnyZeroFP()) &&
+        (match(Op1, m_FSub(m_AnyZeroFP(), m_Value(X))) ||
+         match(Op1, m_FNeg(m_Value(X)))))
+      return X;
 
   // fsub nnan x, x ==> 0.0
   if (FMF.noNaNs() && Op0 == Op1)
Index: llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
@@ -0,0 +1,680 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instsimplify -S | FileCheck %s
+
+;
+; constrained fsub
+;
+
+;
+; fsub X, +0 ==> X
+;
+
+define float @fsub_x_p0_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fsub_x_p0_defaultenv(
+; CHECK-NEXT:    ret float [[A:%.*]]
+;
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_x_p0_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_x_p0_ebmaytrap(
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0:[0-9]+]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+define float @fsub_nnan_x_p0_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_nnan_x_p0_ebmaytrap(
+; CHECK-NEXT:    ret float [[A:%.*]]
+;
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_x_p0_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_x_p0_ebstrict(
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+define float @fsub_nnan_x_p0_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_nnan_x_p0_ebstrict(
+; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[A]]
+;
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+; Test with a fast math flag set but that flag is not "nnan".
+define float @fsub_ninf_x_p0_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_ninf_x_p0_ebstrict(
+; CHECK-NEXT:    [[RET:%.*]] = call ninf float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %ret = call ninf float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+;
+; fsub X, -0 ==> X, when we know X is not -0
+; (fast math flag: nsz)
+;
+
+define float @fold_fsub_nsz_x_n0_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_nsz_x_n0_defaultenv(
+; CHECK-NEXT:    ret float [[A:%.*]]
+;
+  %sub = call nsz float @llvm.experimental.constrained.fsub.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %sub
+}
+
+; Missing nnan: must not fire.
+define float @fold_fsub_nsz_x_n0_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_nsz_x_n0_ebmaytrap(
+; CHECK-NEXT:    [[SUB:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[SUB]]
+;
+  %sub = call nsz float @llvm.experimental.constrained.fsub.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %sub
+}
+
+define float @fold_fsub_nnan_nsz_x_n0_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_nnan_nsz_x_n0_ebmaytrap(
+; CHECK-NEXT:    ret float [[A:%.*]]
+;
+  %sub = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %sub
+}
+
+; Missing nnan: must not fire.
+define float @fold_fsub_nsz_x_n0_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_nsz_x_n0_ebstrict(
+; CHECK-NEXT:    [[SUB:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[SUB]]
+;
+  %sub = call nsz float @llvm.experimental.constrained.fsub.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %sub
+}
+
+define float @fold_fsub_nsz_nnan_x_n0_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_nsz_nnan_x_n0_ebstrict(
+; CHECK-NEXT:    [[SUB:%.*]] = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[A]]
+;
+  %sub = call nsz nnan float @llvm.experimental.constrained.fsub.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %sub
+}
+
+;
+; fsub X, -0 ==> X, when we know X is not -0
+; (No "nsz" flags)
+;
+
+define float @fold_fsub_fabs_x_n0_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_fabs_x_n0_defaultenv(
+; CHECK-NEXT:    [[ABSA:%.*]] = call float @llvm.fabs.f32(float [[A:%.*]])
+; CHECK-NEXT:    ret float [[ABSA]]
+;
+  %absa = call float @llvm.fabs.f32(float %a)
+  %sub = call float @llvm.experimental.constrained.fsub.f32(float %absa, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %sub
+}
+
+; Missing nnan: must not fire.
+define float @fold_fsub_fabs_x_n0_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_fabs_x_n0_ebmaytrap(
+; CHECK-NEXT:    [[ABSA:%.*]] = call float @llvm.fabs.f32(float [[A:%.*]])
+; CHECK-NEXT:    [[SUB:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[ABSA]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[SUB]]
+;
+  %absa = call float @llvm.fabs.f32(float %a)
+  %sub = call float @llvm.experimental.constrained.fsub.f32(float %absa, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %sub
+}
+
+define float @fold_fsub_fabs_nnan_x_n0_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_fabs_nnan_x_n0_ebmaytrap(
+; CHECK-NEXT:    [[ABSA:%.*]] = call float @llvm.fabs.f32(float [[A:%.*]])
+; CHECK-NEXT:    ret float [[ABSA]]
+;
+  %absa = call float @llvm.fabs.f32(float %a)
+  %sub = call nnan float @llvm.experimental.constrained.fsub.f32(float %absa, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %sub
+}
+
+; Missing nnan: must not fire.
+define float @fold_fsub_fabs_x_n0_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_fabs_x_n0_ebstrict(
+; CHECK-NEXT:    [[ABSA:%.*]] = call float @llvm.fabs.f32(float [[A:%.*]])
+; CHECK-NEXT:    [[SUB:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[ABSA]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[SUB]]
+;
+  %absa = call float @llvm.fabs.f32(float %a)
+  %sub = call float @llvm.experimental.constrained.fsub.f32(float %absa, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %sub
+}
+
+define float @fold_fsub_fabs_nnan_x_n0_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fold_fsub_fabs_nnan_x_n0_ebstrict(
+; CHECK-NEXT:    [[ABSA:%.*]] = call float @llvm.fabs.f32(float [[A:%.*]])
+; CHECK-NEXT:    [[SUB:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float [[ABSA]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[ABSA]]
+;
+  %absa = call float @llvm.fabs.f32(float %a)
+  %sub = call nnan float @llvm.experimental.constrained.fsub.f32(float %absa, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %sub
+}
+
+; TODO: This can't fire currently due to missing constrained support:
+define float @fold_fsub_sitofp_x_n0_defaultenv(i32 %a) #0 {
+; CHECK-LABEL: @fold_fsub_sitofp_x_n0_defaultenv(
+; CHECK-NEXT:    [[FPA:%.*]] = call float @llvm.experimental.constrained.sitofp.f32.i32(i32 [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    [[SUB:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[FPA]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[SUB]]
+;
+  %fpa = call float @llvm.experimental.constrained.sitofp.f32.i32(i32 %a, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  %sub = call float @llvm.experimental.constrained.fsub.f32(float %fpa, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %sub
+}
+
+;
+; fsub -0.0, (fneg X) ==> X
+;
+
+define float @fsub_fneg_n0_fnX_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_n0_fnX_defaultenv(
+; CHECK-NEXT:    ret float [[A:%.*]]
+;
+  %nega = fneg float %a
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_fneg_n0_fnX_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_n0_fnX_ebmaytrap(
+; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = fneg float %a
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+define float @fsub_fneg_nnan_n0_fnX_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_nnan_n0_fnX_ebmaytrap(
+; CHECK-NEXT:    ret float [[A:%.*]]
+;
+  %nega = fneg float %a
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_fneg_n0_fnX_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_n0_fnX_ebstrict(
+; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = fneg float %a
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+define float @fsub_fneg_nnan_n0_fnX_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_nnan_n0_fnX_ebstrict(
+; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[A]]
+;
+  %nega = fneg float %a
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+;
+; fsub -0.0, (fsub -0.0, X) ==> X
+; TODO: These generally don't fire because m_FNeg doesn't know about
+; TODO: the constrained intrinsics.
+;
+
+define float @fsub_fsub_n0_fnX_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_n0_fnX_defaultenv(
+; CHECK-NEXT:    [[NEGA:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_fsub_n0_fnX_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_n0_fnX_ebmaytrap(
+; CHECK-NEXT:    [[NEGA:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+define float @fsub_fsub_nnan_n0_fnX_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_nnan_n0_fnX_ebmaytrap(
+; CHECK-NEXT:    [[NEGA:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_fsub_n0_fnX_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_n0_fnX_ebstrict(
+; CHECK-NEXT:    [[NEGA:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+define float @fsub_fsub_nnan_n0_fnX_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_nnan_n0_fnX_ebstrict(
+; CHECK-NEXT:    [[NEGA:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+;
+; fsub 0.0, (fneg X) ==> X if signed zeros are ignored.
+;
+
+define float @fsub_fneg_nsz_p0_fnX_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_nsz_p0_fnX_defaultenv(
+; CHECK-NEXT:    ret float [[A:%.*]]
+;
+  %nega = fneg float %a
+  %ret = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_fneg_nsz_p0_fnX_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_nsz_p0_fnX_ebmaytrap(
+; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = fneg float %a
+  %ret = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+define float @fsub_fneg_nsz_nnan_p0_fnX_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_nsz_nnan_p0_fnX_ebmaytrap(
+; CHECK-NEXT:    ret float [[A:%.*]]
+;
+  %nega = fneg float %a
+  %ret = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_fneg_nsz_p0_fnX_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_nsz_p0_fnX_ebstrict(
+; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = fneg float %a
+  %ret = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+define float @fsub_fneg_nnan_nsz_p0_fnX_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_fneg_nnan_nsz_p0_fnX_ebstrict(
+; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[A]]
+;
+  %nega = fneg float %a
+  %ret = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+;
+; fsub 0.0, (fsub 0.0, X) ==> X if signed zeros are ignored.
+; TODO: These generally don't fire because m_FNeg and m_FSub don't know
+; TODO: about the constrained intrinsics.
+;
+
+define float @fsub_fsub_p0_nsz_fnX_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_p0_nsz_fnX_defaultenv(
+; CHECK-NEXT:    [[NEGA:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  %ret = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_fsub_nsz_p0_fnX_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_nsz_p0_fnX_ebmaytrap(
+; CHECK-NEXT:    [[NEGA:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+define float @fsub_fsub_nnan_nsz_p0_fnX_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_nnan_nsz_p0_fnX_ebmaytrap(
+; CHECK-NEXT:    [[NEGA:%.*]] = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_fsub_nsz_p0_fnX_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_nsz_p0_fnX_ebstrict(
+; CHECK-NEXT:    [[NEGA:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  %ret = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+define float @fsub_fsub_nnan_nsz_p0_fnX_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_fsub_nnan_nsz_p0_fnX_ebstrict(
+; CHECK-NEXT:    [[NEGA:%.*]] = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[A:%.*]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %nega = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %a, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  %ret = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+;
+; fsub nnan x, x ==> 0.0
+;
+
+; Missing nnan: must not fire.
+define float @fsub_x_x_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fsub_x_x_defaultenv(
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float [[A]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %a, float %a, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+define float @fsub_nnan_x_x_defaultenv(float %a) #0 {
+; CHECK-LABEL: @fsub_nnan_x_x_defaultenv(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float %a, float %a, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_x_x_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_x_x_ebmaytrap(
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float [[A]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %a, float %a, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+define float @fsub_nnan_x_x_ebmaytrap(float %a) #0 {
+; CHECK-LABEL: @fsub_nnan_x_x_ebmaytrap(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float %a, float %a, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; Missing nnan: must not fire.
+define float @fsub_x_x_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_x_x_ebstrict(
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float [[A]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %a, float %a, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+define float @fsub_nnan_x_x_ebstrict(float %a) #0 {
+; CHECK-LABEL: @fsub_nnan_x_x_ebstrict(
+; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float [[A]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float %a, float %a, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+;
+; Y - (Y - X) --> X
+; TODO: Missing IR matcher support means these won't fire.
+;
+
+; Missing nsz and reassoc: must not fire
+define float @fsub_fsub_y_x_x_defaultenv(float %x, float %y) #0 {
+; CHECK-LABEL: @fsub_fsub_y_x_x_defaultenv(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y:%.*]], float [[X:%.*]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y]], float [[INNER]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fsub.f32(float %y, float %x, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %y, float %inner, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+define float @fsub_fsub_fmf_y_x_x_defaultenv(float %x, float %y) #0 {
+; CHECK-LABEL: @fsub_fsub_fmf_y_x_x_defaultenv(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y:%.*]], float [[X:%.*]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call reassoc nsz float @llvm.experimental.constrained.fsub.f32(float [[Y]], float [[INNER]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fsub.f32(float %y, float %x, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  %ret = call nsz reassoc float @llvm.experimental.constrained.fsub.f32(float %y, float %inner, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; TODO: Consider how alternate rounding modes can break these transforms.
+
+; The "fpexcept.maytrap" instruction must _not_ be folded into the
+; "fpexcept.ignore" instruction.
+define float @fsub_fsub_fmf_y_x_x_ebmaytrap_defaultenv(float %x, float %y) #0 {
+; CHECK-LABEL: @fsub_fsub_fmf_y_x_x_ebmaytrap_defaultenv(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y:%.*]], float [[X:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call reassoc nsz float @llvm.experimental.constrained.fsub.f32(float [[Y]], float [[INNER]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fsub.f32(float %y, float %x, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call nsz reassoc float @llvm.experimental.constrained.fsub.f32(float %y, float %inner, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; Missing nsz and reassoc: must not fire
+; TODO: Should this ever be allowed?
+define float @fsub_fsub_y_x_x_ebmaytrap(float %x, float %y) #0 {
+; CHECK-LABEL: @fsub_fsub_y_x_x_ebmaytrap(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y:%.*]], float [[X:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y]], float [[INNER]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fsub.f32(float %y, float %x, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %y, float %inner, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; TODO: Should this ever be allowed?
+define float @fsub_fsub_fmf_y_x_x_ebmaytrap(float %x, float %y) #0 {
+; CHECK-LABEL: @fsub_fsub_fmf_y_x_x_ebmaytrap(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y:%.*]], float [[X:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call reassoc nsz float @llvm.experimental.constrained.fsub.f32(float [[Y]], float [[INNER]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fsub.f32(float %y, float %x, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call nsz reassoc float @llvm.experimental.constrained.fsub.f32(float %y, float %inner, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; Missing nsz and reassoc: must not fire
+; TODO: Should this ever be allowed?
+define float @fsub_fsub_y_x_x_ebstrict(float %x, float %y) #0 {
+; CHECK-LABEL: @fsub_fsub_y_x_x_ebstrict(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y:%.*]], float [[X:%.*]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y]], float [[INNER]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fsub.f32(float %y, float %x, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %y, float %inner, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+; TODO: Should this ever be allowed?
+define float @fsub_fsub_fmf_y_x_x_ebstrict(float %x, float %y) #0 {
+; CHECK-LABEL: @fsub_fsub_fmf_y_x_x_ebstrict(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[Y:%.*]], float [[X:%.*]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call reassoc nsz float @llvm.experimental.constrained.fsub.f32(float [[Y]], float [[INNER]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fsub.f32(float %y, float %x, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  %ret = call nsz reassoc float @llvm.experimental.constrained.fsub.f32(float %y, float %inner, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+;
+; (X + Y) - Y --> X
+; TODO: Missing IR matcher support means these won't fire.
+;
+
+; Missing nsz and reassoc: must not fire
+define float @fadd_fsub_x_y_y_defaultenv(float %x, float %y) #0 {
+; CHECK-LABEL: @fadd_fsub_x_y_y_defaultenv(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[X:%.*]], float [[Y:%.*]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[INNER]], float [[Y]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fadd.f32(float %x, float %y, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %inner, float %y, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+define float @fadd_fsub_fmf_x_y_y_defaultenv(float %x, float %y) #0 {
+; CHECK-LABEL: @fadd_fsub_fmf_x_y_y_defaultenv(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[X:%.*]], float [[Y:%.*]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call reassoc nsz float @llvm.experimental.constrained.fsub.f32(float [[INNER]], float [[Y]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fadd.f32(float %x, float %y, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  %ret = call nsz reassoc float @llvm.experimental.constrained.fsub.f32(float %inner, float %y, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; The "fpexcept.maytrap" instruction must _not_ be folded into the
+; "fpexcept.ignore" instruction.
+define float @fadd_fsub_fmf_x_y_y_ebmaytrap_defaultenv(float %x, float %y) #0 {
+; CHECK-LABEL: @fadd_fsub_fmf_x_y_y_ebmaytrap_defaultenv(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[X:%.*]], float [[Y:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call reassoc nsz float @llvm.experimental.constrained.fsub.f32(float [[INNER]], float [[Y]], metadata !"round.tonearest", metadata !"fpexcept.ignore") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fadd.f32(float %x, float %y, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call nsz reassoc float @llvm.experimental.constrained.fsub.f32(float %inner, float %y, metadata !"round.tonearest", metadata !"fpexcept.ignore") #0
+  ret float %ret
+}
+
+; Missing nsz and reassoc: must not fire
+; TODO: Should this ever be allowed?
+define float @fadd_fsub_x_y_y_ebmaytrap(float %x, float %y) #0 {
+; CHECK-LABEL: @fadd_fsub_x_y_y_ebmaytrap(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[X:%.*]], float [[Y:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[INNER]], float [[Y]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fadd.f32(float %x, float %y, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %inner, float %y, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; TODO: Should this ever be allowed?
+define float @fadd_fsub_fmf_x_y_y_ebmaytrap(float %x, float %y) #0 {
+; CHECK-LABEL: @fadd_fsub_fmf_x_y_y_ebmaytrap(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[X:%.*]], float [[Y:%.*]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call reassoc nsz float @llvm.experimental.constrained.fsub.f32(float [[INNER]], float [[Y]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fadd.f32(float %x, float %y, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  %ret = call nsz reassoc float @llvm.experimental.constrained.fsub.f32(float %inner, float %y, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
+  ret float %ret
+}
+
+; Missing nsz and reassoc: must not fire
+; TODO: Should this ever be allowed?
+define float @fadd_fsub_x_y_y_ebstrict(float %x, float %y) #0 {
+; CHECK-LABEL: @fadd_fsub_x_y_y_ebstrict(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[X:%.*]], float [[Y:%.*]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[INNER]], float [[Y]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fadd.f32(float %x, float %y, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  %ret = call float @llvm.experimental.constrained.fsub.f32(float %inner, float %y, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+; TODO: Should this ever be allowed?
+define float @fadd_fsub_fmf_x_y_y_ebstrict(float %x, float %y) #0 {
+; CHECK-LABEL: @fadd_fsub_fmf_x_y_y_ebstrict(
+; CHECK-NEXT:    [[INNER:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[X:%.*]], float [[Y:%.*]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call reassoc nsz float @llvm.experimental.constrained.fsub.f32(float [[INNER]], float [[Y]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    ret float [[RET]]
+;
+  %inner = call float @llvm.experimental.constrained.fadd.f32(float %x, float %y, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  %ret = call nsz reassoc float @llvm.experimental.constrained.fsub.f32(float %inner, float %y, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
+  ret float %ret
+}
+
+declare float @llvm.fabs.f32(float)
+declare <2 x float> @llvm.fabs.v2f32(<2 x float>)
+
+declare float @llvm.experimental.constrained.fadd.f32(float, float, metadata, metadata) #0
+declare float @llvm.experimental.constrained.fsub.f32(float, float, metadata, metadata) #0
+
+declare float @llvm.experimental.constrained.sitofp.f32.i32(i32, metadata, metadata) #0
+
+attributes #0 = { strictfp }