diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -8223,22 +8223,24 @@
   SDValue Arg = Op.getOperand(0);
   SDValue TrigVal;
 
-  // TODO: Should this propagate fast-math-flags?
+  // Propagate fast-math flags so that the multiply we introduce can be folded
+  // if Arg is already the result of a multiply by constant.
+  auto Flags = Op->getFlags();
 
   SDValue OneOver2Pi = DAG.getConstantFP(0.5 * numbers::inv_pi, DL, VT);
 
   if (Subtarget->hasTrigReducedRange()) {
-    SDValue MulVal = DAG.getNode(ISD::FMUL, DL, VT, Arg, OneOver2Pi);
-    TrigVal = DAG.getNode(AMDGPUISD::FRACT, DL, VT, MulVal);
+    SDValue MulVal = DAG.getNode(ISD::FMUL, DL, VT, Arg, OneOver2Pi, Flags);
+    TrigVal = DAG.getNode(AMDGPUISD::FRACT, DL, VT, MulVal, Flags);
   } else {
-    TrigVal = DAG.getNode(ISD::FMUL, DL, VT, Arg, OneOver2Pi);
+    TrigVal = DAG.getNode(ISD::FMUL, DL, VT, Arg, OneOver2Pi, Flags);
   }
 
   switch (Op.getOpcode()) {
   case ISD::FCOS:
-    return DAG.getNode(AMDGPUISD::COS_HW, SDLoc(Op), VT, TrigVal);
+    return DAG.getNode(AMDGPUISD::COS_HW, SDLoc(Op), VT, TrigVal, Flags);
   case ISD::FSIN:
-    return DAG.getNode(AMDGPUISD::SIN_HW, SDLoc(Op), VT, TrigVal);
+    return DAG.getNode(AMDGPUISD::SIN_HW, SDLoc(Op), VT, TrigVal, Flags);
   default:
     llvm_unreachable("Wrong trig opcode");
   }
diff --git a/llvm/test/CodeGen/AMDGPU/llvm.sin.ll b/llvm/test/CodeGen/AMDGPU/llvm.sin.ll
--- a/llvm/test/CodeGen/AMDGPU/llvm.sin.ll
+++ b/llvm/test/CodeGen/AMDGPU/llvm.sin.ll
@@ -51,6 +51,21 @@
   ret void
 }
 
+; FUNC-LABEL: {{^}}fmf_sin_3x_f32:
+; GCN-NOT: v_add_f32
+; GCN: 0x3ef47644
+; GCN: v_mul_f32
+; SICIVI: v_fract_f32
+; GFX9-NOT: v_fract_f32
+; GCN: v_sin_f32
+; GCN-NOT: v_sin_f32
+define amdgpu_kernel void @fmf_sin_3x_f32(float addrspace(1)* %out, float %x) #1 {
+  %y = fmul reassoc float 3.0, %x
+  %sin = call reassoc float @llvm.sin.f32(float %y)
+  store float %sin, float addrspace(1)* %out
+  ret void
+}
+
 ; FUNC-LABEL: {{^}}safe_sin_2x_f32:
 ; GCN: v_add_f32
 ; GCN: v_mul_f32
@@ -80,6 +95,63 @@
   ret void
 }
 
+; FUNC-LABEL: {{^}}fmf_sin_2x_f32:
+; GCN-NOT: v_add_f32
+; GCN: 0x3ea2f983
+; GCN: v_mul_f32
+; SICIVI: v_fract_f32
+; GFX9-NOT: v_fract_f32
+; GCN: v_sin_f32
+; GCN-NOT: v_sin_f32
+define amdgpu_kernel void @fmf_sin_2x_f32(float addrspace(1)* %out, float %x) #1 {
+  %y = fmul reassoc float 2.0, %x
+  %sin = call reassoc float @llvm.sin.f32(float %y)
+  store float %sin, float addrspace(1)* %out
+  ret void
+}
+
+; FUNC-LABEL: {{^}}safe_sin_cancel_f32:
+; GCN: v_mul_f32
+; GCN: v_mul_f32
+; SICIVI: v_fract_f32
+; GFX9-NOT: v_fract_f32
+; GCN: v_sin_f32
+; GCN-NOT: v_sin_f32
+define amdgpu_kernel void @safe_sin_cancel_f32(float addrspace(1)* %out, float %x) #1 {
+  %y = fmul float 0x401921FB60000000, %x
+  %sin = call float @llvm.sin.f32(float %y)
+  store float %sin, float addrspace(1)* %out
+  ret void
+}
+
+; FUNC-LABEL: {{^}}unsafe_sin_cancel_f32:
+; GCN-NOT: v_add_f32
+; GCN-NOT: v_mul_f32
+; SICIVI: v_fract_f32
+; GFX9-NOT: v_fract_f32
+; GCN: v_sin_f32
+; GCN-NOT: v_sin_f32
+define amdgpu_kernel void @unsafe_sin_cancel_f32(float addrspace(1)* %out, float %x) #2 {
+  %y = fmul float 0x401921FB60000000, %x
+  %sin = call float @llvm.sin.f32(float %y)
+  store float %sin, float addrspace(1)* %out
+  ret void
+}
+
+; FUNC-LABEL: {{^}}fmf_sin_cancel_f32:
+; GCN-NOT: v_add_f32
+; GCN-NOT: v_mul_f32
+; SICIVI: v_fract_f32
+; GFX9-NOT: v_fract_f32
+; GCN: v_sin_f32
+; GCN-NOT: v_sin_f32
+define amdgpu_kernel void @fmf_sin_cancel_f32(float addrspace(1)* %out, float %x) #1 {
+  %y = fmul reassoc float 0x401921FB60000000, %x
+  %sin = call reassoc float @llvm.sin.f32(float %y)
+  store float %sin, float addrspace(1)* %out
+  ret void
+}
+
 ; FUNC-LABEL: {{^}}sin_v4f32:
 ; EG: SIN * T{{[0-9]+\.[XYZW], PV\.[XYZW]}}
 ; EG: SIN * T{{[0-9]+\.[XYZW], PV\.[XYZW]}}