Index: llvm/include/llvm/IR/FPEnv.h
===================================================================
--- llvm/include/llvm/IR/FPEnv.h
+++ llvm/include/llvm/IR/FPEnv.h
@@ -58,5 +58,11 @@
 inline bool isDefaultFPEnvironment(fp::ExceptionBehavior EB, RoundingMode RM) {
   return EB == fp::ebIgnore && RM == RoundingMode::NearestTiesToEven;
 }
+
+/// Returns true if the rounding mode RM may be QRM at compile time or
+/// at run time.
+inline bool RoundingModeMayBe(RoundingMode RM, RoundingMode QRM) {
+  return RM == QRM || RM == RoundingMode::Dynamic;
+}
 }
 #endif
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4902,17 +4902,22 @@
   if (Constant *C = simplifyFPOp({Op0, Op1}, FMF, Q, ExBehavior, Rounding))
     return C;
 
-  if (!isDefaultFPEnvironment(ExBehavior, Rounding))
-    return nullptr;
-
   // fadd X, -0 ==> X
-  if (match(Op1, m_NegZeroFP()))
-    return Op0;
+  if (isDefaultFPEnvironment(ExBehavior, Rounding) ||
+      (!RoundingModeMayBe(Rounding, RoundingMode::TowardNegative) &&
+       (ExBehavior != fp::ebStrict || FMF.noNaNs())))
+    if (match(Op1, m_NegZeroFP()))
+      return Op0;
 
   // fadd X, 0 ==> X, when we know X is not -0
-  if (match(Op1, m_PosZeroFP()) &&
-      (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
-    return Op0;
+  if (isDefaultFPEnvironment(ExBehavior, Rounding) ||
+      (ExBehavior != fp::ebStrict || FMF.noNaNs()))
+    if (match(Op1, m_PosZeroFP()) &&
+        (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
+      return Op0;
+
+  if (!isDefaultFPEnvironment(ExBehavior, Rounding))
+    return nullptr;
 
   // With nnan: -X + X --> 0.0 (and commuted variant)
   // We don't have to explicitly exclude infinities (ninf): INF + -INF == NaN.
Index: llvm/test/Transforms/InstSimplify/strictfp-fadd.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/strictfp-fadd.ll
+++ llvm/test/Transforms/InstSimplify/strictfp-fadd.ll
@@ -27,8 +27,7 @@
 
 define float @fadd_x_n0_ebmaytrap(float %a) #0 {
 ; CHECK-LABEL: @fadd_x_n0_ebmaytrap(
-; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0:[0-9]+]]
-; CHECK-NEXT:    ret float [[RET]]
+; CHECK-NEXT:    ret float [[A:%.*]]
 ;
   %ret = call float @llvm.experimental.constrained.fadd.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret float %ret
@@ -36,8 +35,7 @@
 
 define <2 x float> @fadd_vec_x_n0_ebmaytrap(<2 x float> %a) #0 {
 ; CHECK-LABEL: @fadd_vec_x_n0_ebmaytrap(
-; CHECK-NEXT:    [[RET:%.*]] = call <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> [[A:%.*]], <2 x float> <float -0.000000e+00, float -0.000000e+00>, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
-; CHECK-NEXT:    ret <2 x float> [[RET]]
+; CHECK-NEXT:    ret <2 x float> [[A:%.*]]
 ;
   %ret = call <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> %a, <2 x float><float -0.0, float -0.0>, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret <2 x float> %ret
@@ -45,7 +43,7 @@
 
 define float @fadd_x_n0_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fadd_x_n0_ebstrict(
-; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
+; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0:[0-9]+]]
 ; CHECK-NEXT:    ret float [[RET]]
 ;
   %ret = call float @llvm.experimental.constrained.fadd.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
@@ -101,8 +99,7 @@
 ; Test one of the remaining rounding modes and the rest will be fine.
 define float @fadd_x_n0_towardzero(float %a) #0 {
 ; CHECK-LABEL: @fadd_x_n0_towardzero(
-; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.towardzero", metadata !"fpexcept.ignore") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[RET]]
+; CHECK-NEXT:    ret float [[A:%.*]]
 ;
   %ret = call float @llvm.experimental.constrained.fadd.f32(float %a, float -0.0, metadata !"round.towardzero", metadata !"fpexcept.ignore") #0
   ret float %ret
@@ -112,8 +109,7 @@
 ; Test one of the remaining rounding modes and the rest will be fine.
 define <2 x float> @fadd_vec_x_n0_towardzero(<2 x float> %a) #0 {
 ; CHECK-LABEL: @fadd_vec_x_n0_towardzero(
-; CHECK-NEXT:    [[RET:%.*]] = call <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> [[A:%.*]], <2 x float> <float -0.000000e+00, float -0.000000e+00>, metadata !"round.towardzero", metadata !"fpexcept.ignore") #[[ATTR0]]
-; CHECK-NEXT:    ret <2 x float> [[RET]]
+; CHECK-NEXT:    ret <2 x float> [[A:%.*]]
 ;
   %ret = call <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> %a, <2 x float><float -0.0, float -0.0>, metadata !"round.towardzero", metadata !"fpexcept.ignore") #0
   ret <2 x float> %ret
@@ -122,7 +118,7 @@
 define float @fadd_nnan_x_n0_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fadd_nnan_x_n0_ebstrict(
 ; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[RET]]
+; CHECK-NEXT:    ret float [[A]]
 ;
   %ret = call nnan float @llvm.experimental.constrained.fadd.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %ret
@@ -131,7 +127,7 @@
 define <2 x float> @fadd_vec_nnan_x_n0_ebstrict(<2 x float> %a) #0 {
 ; CHECK-LABEL: @fadd_vec_nnan_x_n0_ebstrict(
 ; CHECK-NEXT:    [[RET:%.*]] = call nnan <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> [[A:%.*]], <2 x float> <float -0.000000e+00, float -0.000000e+00>, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
-; CHECK-NEXT:    ret <2 x float> [[RET]]
+; CHECK-NEXT:    ret <2 x float> [[A]]
 ;
   %ret = call nnan <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> %a, <2 x float><float -0.0, float -0.0>, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret <2 x float> %ret
@@ -215,8 +211,7 @@
 
 define float @fold_fadd_nsz_x_0_ebmaytrap(float %a) #0 {
 ; CHECK-LABEL: @fold_fadd_nsz_x_0_ebmaytrap(
-; CHECK-NEXT:    [[ADD:%.*]] = call nsz float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[ADD]]
+; CHECK-NEXT:    ret float [[A:%.*]]
 ;
   %add = call nsz float @llvm.experimental.constrained.fadd.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret float %add
@@ -224,8 +219,7 @@
 
 define <2 x float> @fold_fadd_vec_nsz_x_0_ebmaytrap(<2 x float> %a) #0 {
 ; CHECK-LABEL: @fold_fadd_vec_nsz_x_0_ebmaytrap(
-; CHECK-NEXT:    [[ADD:%.*]] = call nsz <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> [[A:%.*]], <2 x float> zeroinitializer, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
-; CHECK-NEXT:    ret <2 x float> [[ADD]]
+; CHECK-NEXT:    ret <2 x float> [[A:%.*]]
 ;
   %add = call nsz <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> %a, <2 x float> zeroinitializer, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret <2 x float> %add
@@ -252,7 +246,7 @@
 define float @fold_fadd_nsz_nnan_x_0_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fold_fadd_nsz_nnan_x_0_ebstrict(
 ; CHECK-NEXT:    [[ADD:%.*]] = call nnan nsz float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[ADD]]
+; CHECK-NEXT:    ret float [[A]]
 ;
   %add = call nsz nnan float @llvm.experimental.constrained.fadd.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %add
@@ -261,7 +255,7 @@
 define <2 x float> @fold_fadd_vec_nsz_nnan_x_0_ebstrict(<2 x float> %a) #0 {
 ; CHECK-LABEL: @fold_fadd_vec_nsz_nnan_x_0_ebstrict(
 ; CHECK-NEXT:    [[ADD:%.*]] = call nnan nsz <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> [[A:%.*]], <2 x float> zeroinitializer, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
-; CHECK-NEXT:    ret <2 x float> [[ADD]]
+; CHECK-NEXT:    ret <2 x float> [[A]]
 ;
   %add = call nsz nnan <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> %a, <2 x float> zeroinitializer, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret <2 x float> %add