[Reassociate] Don't reassociate when mixing regular and fast-math FP

instructions.  Inlining might cause such cases and it's not valid to
reassociate floating-point instructions without the unsafe algebra flag.

Patch by Mehdi Amini <mehdi_amini@apple.com>!

llvm-svn: 221462

2 files changed, 27 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index 0d5ad7311fb..02cf708311b 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -237,7 +237,9 @@ FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
 /// opcode and if it only has one use.
 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
   if (V->hasOneUse() && isa<Instruction>(V) &&
-      cast<Instruction>(V)->getOpcode() == Opcode)
+      cast<Instruction>(V)->getOpcode() == Opcode &&
+      (!isa<FPMathOperator>(V) ||
+       cast<Instruction>(V)->hasUnsafeAlgebra()))
     return cast<BinaryOperator>(V);
   return nullptr;
 }
@@ -246,7 +248,9 @@ static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode1,
                                         unsigned Opcode2) {
   if (V->hasOneUse() && isa<Instruction>(V) &&
       (cast<Instruction>(V)->getOpcode() == Opcode1 ||
-       cast<Instruction>(V)->getOpcode() == Opcode2))
+       cast<Instruction>(V)->getOpcode() == Opcode2) &&
+      (!isa<FPMathOperator>(V) ||
+       cast<Instruction>(V)->hasUnsafeAlgebra()))
     return cast<BinaryOperator>(V);
   return nullptr;
 }
@@ -662,7 +666,9 @@ static bool LinearizeExprTree(BinaryOperator *I,
       // expression.  This means that it can safely be modified.  See if we
       // can usefully morph it into an expression of the right kind.
       assert((!isa<Instruction>(Op) ||
-              cast<Instruction>(Op)->getOpcode() != Opcode) &&
+              cast<Instruction>(Op)->getOpcode() != Opcode
+              || (isa<FPMathOperator>(Op) &&
+                  !cast<Instruction>(Op)->hasUnsafeAlgebra())) &&
              "Should have been handled above!");
       assert(Op->hasOneUse() && "Has uses outside the expression tree!");
 
diff --git a/llvm/test/Transforms/Reassociate/mixed-fast-nonfast-fp.ll b/llvm/test/Transforms/Reassociate/mixed-fast-nonfast-fp.ll
new file mode 100644
index 00000000000..f51c0c17fe7
--- /dev/null
+++ b/llvm/test/Transforms/Reassociate/mixed-fast-nonfast-fp.ll
@@ -0,0 +1,18 @@
+; RUN: opt -reassociate %s -S | FileCheck %s
+
+define float @foo(float %a,float %b, float %c) {
+; CHECK: %mul3 = fmul float %a, %b
+; CHECK-NEXT: fmul fast float %c, 2.000000e+00
+; CHECK-NEXT: fadd fast float %factor, %b
+; CHECK-NEXT: fmul fast float %tmp1, %a
+; CHECK-NEXT: fadd fast float %tmp2, %mul3
+; CHECK-NEXT: ret float
+  %mul1 = fmul fast float %a, %c
+  %mul2 = fmul fast float %a, %b
+  %mul3 = fmul float %a, %b
+  %mul4 = fmul fast float %a, %c
+  %add1 = fadd fast  float %mul1, %mul3
+  %add2 = fadd  fast float %mul4, %mul2
+  %add3 = fadd fast float %add1, %add2
+  ret float %add3
+}