2 files changed, 53 insertions, 4 deletions
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 8ee4d3f7be1..a6430383117 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -113,6 +113,22 @@ static bool CanElideOverflowCheck(const ASTContext &Ctx, const BinOpInfo &Op) {
          (2 * Ctx.getTypeSize(RHSTy)) < PromotedSize;
 }
 
+/// Update the FastMathFlags of LLVM IR from the FPOptions in LangOptions.
+static void updateFastMathFlags(llvm::FastMathFlags &FMF,
+                                FPOptions FPFeatures) {
+  FMF.setAllowContract(FPFeatures.allowFPContractAcrossStatement());
+}
+
+/// Propagate fast-math flags from \p Op to the instruction in \p V.
+static Value *propagateFMFlags(Value *V, const BinOpInfo &Op) {
+  if (auto *I = dyn_cast<llvm::Instruction>(V)) {
+    llvm::FastMathFlags FMF = I->getFastMathFlags();
+    updateFastMathFlags(FMF, Op.FPFeatures);
+    I->setFastMathFlags(FMF);
+  }
+  return V;
+}
+
 class ScalarExprEmitter
   : public StmtVisitor<ScalarExprEmitter, Value*> {
   CodeGenFunction &CGF;
@@ -553,8 +569,10 @@ public:
         !CanElideOverflowCheck(CGF.getContext(), Ops))
       return EmitOverflowCheckedBinOp(Ops);
 
-    if (Ops.LHS->getType()->isFPOrFPVectorTy())
-      return Builder.CreateFMul(Ops.LHS, Ops.RHS, "mul");
+    if (Ops.LHS->getType()->isFPOrFPVectorTy()) {
+      Value *V = Builder.CreateFMul(Ops.LHS, Ops.RHS, "mul");
+      return propagateFMFlags(V, Ops);
+    }
     return Builder.CreateMul(Ops.LHS, Ops.RHS, "mul");
   }
   /// Create a binary op that checks for overflow.
@@ -2722,7 +2740,8 @@ Value *ScalarExprEmitter::EmitAdd(const BinOpInfo &op) {
     if (Value *FMulAdd = tryEmitFMulAdd(op, CGF, Builder))
       return FMulAdd;
 
-    return Builder.CreateFAdd(op.LHS, op.RHS, "add");
+    Value *V = Builder.CreateFAdd(op.LHS, op.RHS, "add");
+    return propagateFMFlags(V, op);
   }
 
   return Builder.CreateAdd(op.LHS, op.RHS, "add");
@@ -2755,7 +2774,8 @@ Value *ScalarExprEmitter::EmitSub(const BinOpInfo &op) {
       // Try to form an fmuladd.
       if (Value *FMulAdd = tryEmitFMulAdd(op, CGF, Builder, true))
         return FMulAdd;
-      return Builder.CreateFSub(op.LHS, op.RHS, "sub");
+      Value *V = Builder.CreateFSub(op.LHS, op.RHS, "sub");
+      return propagateFMFlags(V, op);
     }
 
     return Builder.CreateSub(op.LHS, op.RHS, "sub");
diff --git a/clang/test/CodeGen/ffp-contract-fast-option.cpp b/clang/test/CodeGen/ffp-contract-fast-option.cpp
new file mode 100644
index 00000000000..3db93de107c
--- /dev/null
+++ b/clang/test/CodeGen/ffp-contract-fast-option.cpp
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -O3 -ffp-contract=fast -triple %itanium_abi_triple -emit-llvm -o - %s | FileCheck %s
+
+float fp_contract_1(float a, float b, float c) {
+  // CHECK-LABEL: fp_contract_1fff(
+  // CHECK: fmul contract float
+  // CHECK: fadd contract float
+  return a * b + c;
+}
+
+float fp_contract_2(float a, float b, float c) {
+  // CHECK-LABEL: fp_contract_2fff(
+  // CHECK: fmul contract float
+  // CHECK: fsub contract float
+  return a * b - c;
+}
+
+void fp_contract_3(float *a, float b, float c) {
+  // CHECK-LABEL: fp_contract_3Pfff(
+  // CHECK: fmul contract float
+  // CHECK: fadd contract float
+  a[0] += b * c;
+}
+
+void fp_contract_4(float *a, float b, float c) {
+  // CHECK-LABEL: fp_contract_4Pfff(
+  // CHECK: fmul contract float
+  // CHECK: fsub contract float
+  a[0] -= b * c;
+}