Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -4623,11 +4623,18 @@
 
     break;
   }
-  case Instruction::FDiv: {
-    // X / X is always exactly 1.0 or a NaN.
+  case Instruction::FDiv:
+  case Instruction::FRem: {
     if (Op->getOperand(0) == Op->getOperand(1)) {
       // TODO: Could filter out snan if we inspect the operand
-      Known.KnownFPClasses = fcNan | fcPosNormal;
+      if (Op->getOpcode() == Instruction::FDiv) {
+        // X / X is always exactly 1.0 or a NaN.
+        Known.KnownFPClasses = fcNan | fcPosNormal;
+      } else {
+        // X % X is always exactly 0.0 or a NaN.
+        Known.KnownFPClasses = fcNan | fcPosZero;
+      }
+
       break;
     }
 
@@ -4637,7 +4644,6 @@
     if (!WantNan && !WantNegative)
       break;
 
-    // TODO: FRem
     KnownFPClass KnownLHS, KnownRHS;
 
     computeKnownFPClass(Op->getOperand(1), DemandedElts,
@@ -4650,19 +4656,29 @@
 
     if (KnowSomethingUseful) {
       computeKnownFPClass(Op->getOperand(0), DemandedElts,
-                          fcNan | fcInf | fcZero |
+                          fcNan | fcInf | fcZero | fcSubnormal |
                               KnownFPClass::OrderedLessThanZeroMask,
                           KnownLHS, Depth + 1, Q, TLI);
     }
 
     const Function *F = cast<Instruction>(Op)->getFunction();
 
-    // Only 0/0, Inf/Inf, Inf REM x and x REM 0 produce NaN.
-    if (KnownLHS.isKnownNeverNaN() && KnownRHS.isKnownNeverNaN() &&
-        (KnownLHS.isKnownNeverInfinity() || KnownRHS.isKnownNeverInfinity()) &&
-        (KnownLHS.isKnownNeverLogicalZero(*F, Op->getType()) ||
-         KnownRHS.isKnownNeverLogicalZero(*F, Op->getType()))) {
-      Known.knownNot(fcNan);
+    if (Op->getOpcode() == Instruction::FDiv) {
+      // Only 0/0, Inf/Inf, Inf REM x and x REM 0 produce NaN.
+      if (KnownLHS.isKnownNeverNaN() && KnownRHS.isKnownNeverNaN() &&
+          (KnownLHS.isKnownNeverInfinity() ||
+           KnownRHS.isKnownNeverInfinity()) &&
+          (KnownLHS.isKnownNeverLogicalZero(*F, Op->getType()) ||
+           KnownRHS.isKnownNeverLogicalZero(*F, Op->getType()))) {
+        Known.knownNot(fcNan);
+      }
+    } else {
+      // Inf REM x and x REM 0 produce NaN.
+      if (KnownLHS.isKnownNeverNaN() && KnownRHS.isKnownNeverNaN() &&
+          KnownLHS.isKnownNeverInfinity() &&
+          KnownRHS.isKnownNeverLogicalZero(*F, Op->getType())) {
+        Known.knownNot(fcNan);
+      }
     }
 
     // X / -0.0 is -Inf (or NaN).
Index: llvm/test/Transforms/Attributor/nofpclass-frem.ll
===================================================================
--- llvm/test/Transforms/Attributor/nofpclass-frem.ll
+++ llvm/test/Transforms/Attributor/nofpclass-frem.ll
@@ -82,7 +82,7 @@
 }
 
 define float @ret_frem_ieee_nonan_noinf__nonan_nozero(float nofpclass(nan inf) %arg0, float nofpclass(nan zero) %arg1) #0 {
-; CHECK-LABEL: define float @ret_frem_ieee_nonan_noinf__nonan_nozero
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_ieee_nonan_noinf__nonan_nozero
 ; CHECK-SAME: (float nofpclass(nan inf) [[ARG0:%.*]], float nofpclass(nan zero) [[ARG1:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -122,7 +122,7 @@
 }
 
 define float @ret_frem_daz_nonan_noinf__nonan_nozero_nosub(float nofpclass(nan inf) %arg0, float nofpclass(nan zero sub) %arg1) #1 {
-; CHECK-LABEL: define float @ret_frem_daz_nonan_noinf__nonan_nozero_nosub
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_daz_nonan_noinf__nonan_nozero_nosub
 ; CHECK-SAME: (float nofpclass(nan inf) [[ARG0:%.*]], float nofpclass(nan zero sub) [[ARG1:%.*]]) #[[ATTR1]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -142,7 +142,7 @@
 }
 
 define float @ret_frem_ieee_nonan_noinf_nozero__nonan_noinf_nozero(float nofpclass(nan inf zero) %arg0, float nofpclass(nan inf zero) %arg1) #0 {
-; CHECK-LABEL: define float @ret_frem_ieee_nonan_noinf_nozero__nonan_noinf_nozero
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_ieee_nonan_noinf_nozero__nonan_noinf_nozero
 ; CHECK-SAME: (float nofpclass(nan inf zero) [[ARG0:%.*]], float nofpclass(nan inf zero) [[ARG1:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -202,7 +202,7 @@
 }
 
 define float @ret_frem_ieee_nonan_noinf_noinf__nonan_noinf_nozero(float nofpclass(nan inf) %arg0, float nofpclass(nan inf zero) %arg1) #0 {
-; CHECK-LABEL: define float @ret_frem_ieee_nonan_noinf_noinf__nonan_noinf_nozero
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_ieee_nonan_noinf_noinf__nonan_noinf_nozero
 ; CHECK-SAME: (float nofpclass(nan inf) [[ARG0:%.*]], float nofpclass(nan inf zero) [[ARG1:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -232,7 +232,7 @@
 }
 
 define float @ret_frem_ieee_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub(float nofpclass(nan inf zero sub) %arg0, float nofpclass(nan inf zero sub) %arg1) #0 {
-; CHECK-LABEL: define float @ret_frem_ieee_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_ieee_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub
 ; CHECK-SAME: (float nofpclass(nan inf zero sub) [[ARG0:%.*]], float nofpclass(nan inf zero sub) [[ARG1:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -243,7 +243,7 @@
 
 ; Denormal mode doesn't matter because sources are nofpclass(sub)
 define float @ret_frem_daz_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub(float nofpclass(nan inf zero sub) %arg0, float nofpclass(nan inf zero sub) %arg1) #1 {
-; CHECK-LABEL: define float @ret_frem_daz_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_daz_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub
 ; CHECK-SAME: (float nofpclass(nan inf zero sub) [[ARG0:%.*]], float nofpclass(nan inf zero sub) [[ARG1:%.*]]) #[[ATTR1]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -253,7 +253,7 @@
 }
 
 define float @ret_frem_dapz_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub(float nofpclass(nan inf zero sub) %arg0, float nofpclass(nan inf zero sub) %arg1) #2 {
-; CHECK-LABEL: define float @ret_frem_dapz_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_dapz_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub
 ; CHECK-SAME: (float nofpclass(nan inf zero sub) [[ARG0:%.*]], float nofpclass(nan inf zero sub) [[ARG1:%.*]]) #[[ATTR2]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -263,7 +263,7 @@
 }
 
 define float @ret_frem_dynamic_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub(float nofpclass(nan inf zero sub) %arg0, float nofpclass(nan inf zero sub) %arg1) #3 {
-; CHECK-LABEL: define float @ret_frem_dynamic_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_dynamic_nonan_noinf_nozero_nosub__nonan_noinf_nozero_nosub
 ; CHECK-SAME: (float nofpclass(nan inf zero sub) [[ARG0:%.*]], float nofpclass(nan inf zero sub) [[ARG1:%.*]]) #[[ATTR3]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -274,7 +274,7 @@
 
 ; Missing no-subnormal on lhs
 define float @ret_frem_daz_nonan_noinf_nozero__nonan_noinf_nozero_nosub(float nofpclass(nan inf zero) %arg0, float nofpclass(nan inf zero sub) %arg1) #1 {
-; CHECK-LABEL: define float @ret_frem_daz_nonan_noinf_nozero__nonan_noinf_nozero_nosub
+; CHECK-LABEL: define nofpclass(nan) float @ret_frem_daz_nonan_noinf_nozero__nonan_noinf_nozero_nosub
 ; CHECK-SAME: (float nofpclass(nan inf zero) [[ARG0:%.*]], float nofpclass(nan inf zero sub) [[ARG1:%.*]]) #[[ATTR1]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -356,7 +356,7 @@
 }
 
 define float @ret_frem_same_operands(float %arg) #0 {
-; CHECK-LABEL: define float @ret_frem_same_operands
+; CHECK-LABEL: define nofpclass(inf nzero sub norm) float @ret_frem_same_operands
 ; CHECK-SAME: (float [[ARG:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG]], [[ARG]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -366,7 +366,7 @@
 }
 
 define float @ret_frem_same_operands_nosnan(float nofpclass(snan) %arg) #0 {
-; CHECK-LABEL: define float @ret_frem_same_operands_nosnan
+; CHECK-LABEL: define nofpclass(inf nzero sub norm) float @ret_frem_same_operands_nosnan
 ; CHECK-SAME: (float nofpclass(snan) [[ARG:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG]], [[ARG]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -376,7 +376,7 @@
 }
 
 define float @ret_frem_same_operands_noqnan(float nofpclass(qnan) %arg) #0 {
-; CHECK-LABEL: define float @ret_frem_same_operands_noqnan
+; CHECK-LABEL: define nofpclass(inf nzero sub norm) float @ret_frem_same_operands_noqnan
 ; CHECK-SAME: (float nofpclass(qnan) [[ARG:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG]], [[ARG]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -386,7 +386,7 @@
 }
 
 define float @ret_frem_same_operands_nonan(float nofpclass(nan) %arg) #0 {
-; CHECK-LABEL: define float @ret_frem_same_operands_nonan
+; CHECK-LABEL: define nofpclass(inf nzero sub norm) float @ret_frem_same_operands_nonan
 ; CHECK-SAME: (float nofpclass(nan) [[ARG:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG]], [[ARG]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -436,7 +436,7 @@
 }
 
 define float @ret_frem_no_neg_nzero(float nofpclass(ninf nsub nnorm nzero) %arg0, float nofpclass(ninf nsub nnorm nzero) %arg1) #0 {
-; CHECK-LABEL: define float @ret_frem_no_neg_nzero
+; CHECK-LABEL: define nofpclass(ninf nzero nsub nnorm) float @ret_frem_no_neg_nzero
 ; CHECK-SAME: (float nofpclass(ninf nzero nsub nnorm) [[ARG0:%.*]], float nofpclass(ninf nzero nsub nnorm) [[ARG1:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]
@@ -456,7 +456,7 @@
 }
 
 define float @ret_frem_no_neg_no_zero_rhs(float nofpclass(ninf nsub nnorm nzero) %arg0, float nofpclass(ninf nsub nnorm zero) %arg1) #0 {
-; CHECK-LABEL: define float @ret_frem_no_neg_no_zero_rhs
+; CHECK-LABEL: define nofpclass(ninf nzero nsub nnorm) float @ret_frem_no_neg_no_zero_rhs
 ; CHECK-SAME: (float nofpclass(ninf nzero nsub nnorm) [[ARG0:%.*]], float nofpclass(ninf zero nsub nnorm) [[ARG1:%.*]]) #[[ATTR0]] {
 ; CHECK-NEXT:    [[FREM:%.*]] = frem float [[ARG0]], [[ARG1]]
 ; CHECK-NEXT:    ret float [[FREM]]