r254573 - change an assert when generating fmuladd to an ordinary 'if' check (PR25719)

[Sanjay Patel via cfe-commits]

Author: spatel
Date: Wed Dec  2 19:25:12 2015
New Revision: 254573

URL: http://llvm.org/viewvc/llvm-project?rev=254573&view=rev
Log:
change an assert when generating fmuladd to an ordinary 'if' check (PR25719)

We don't want to generate fmuladd if there's a use of the fmul expression, but this shouldn't be an assert.

The test case is derived from the commit message for r253337:
http://reviews.llvm.org/rL253337

That commit reverted r253269:
http://reviews.llvm.org/rL253269

...but the bug exists independently of the default fp-contract setting. It just became easier to hit with that change.

PR25719:
https://llvm.org/bugs/show_bug.cgi?id=25719

Differential Revision: http://reviews.llvm.org/D15165


Modified:
    cfe/trunk/lib/CodeGen/CGExprScalar.cpp
    cfe/trunk/test/CodeGen/fp-contract-pragma.cpp

Modified: cfe/trunk/lib/CodeGen/CGExprScalar.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGExprScalar.cpp?rev=254573&r1=254572&r2=254573&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGExprScalar.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGExprScalar.cpp Wed Dec  2 19:25:12 2015
@@ -2564,19 +2564,17 @@ static Value* tryEmitFMulAdd(const BinOp
     return nullptr;
 
   // We have a potentially fusable op. Look for a mul on one of the operands.
-  if (llvm::BinaryOperator* LHSBinOp = dyn_cast<llvm::BinaryOperator>(op.LHS)) {
-    if (LHSBinOp->getOpcode() == llvm::Instruction::FMul) {
-      assert(LHSBinOp->getNumUses() == 0 &&
-             "Operations with multiple uses shouldn't be contracted.");
+  // Also, make sure that the mul result isn't used directly. In that case,
+  // there's no point creating a muladd operation.
+  if (auto *LHSBinOp = dyn_cast<llvm::BinaryOperator>(op.LHS)) {
+    if (LHSBinOp->getOpcode() == llvm::Instruction::FMul &&
+        LHSBinOp->use_empty())
       return buildFMulAdd(LHSBinOp, op.RHS, CGF, Builder, false, isSub);
-    }
-  } else if (llvm::BinaryOperator* RHSBinOp =
-               dyn_cast<llvm::BinaryOperator>(op.RHS)) {
-    if (RHSBinOp->getOpcode() == llvm::Instruction::FMul) {
-      assert(RHSBinOp->getNumUses() == 0 &&
-             "Operations with multiple uses shouldn't be contracted.");
+  }
+  if (auto *RHSBinOp = dyn_cast<llvm::BinaryOperator>(op.RHS)) {
+    if (RHSBinOp->getOpcode() == llvm::Instruction::FMul &&
+        RHSBinOp->use_empty())
       return buildFMulAdd(RHSBinOp, op.LHS, CGF, Builder, isSub, false);
-    }
   }
 
   return nullptr;

Modified: cfe/trunk/test/CodeGen/fp-contract-pragma.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/fp-contract-pragma.cpp?rev=254573&r1=254572&r2=254573&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/fp-contract-pragma.cpp (original)
+++ cfe/trunk/test/CodeGen/fp-contract-pragma.cpp Wed Dec  2 19:25:12 2015
@@ -62,3 +62,15 @@ float fp_contract_6(float a, float b, fl
   return a * b + c;
 }
 
+// If the multiply has multiple uses, don't produce fmuladd.
+// This used to assert (PR25719):
+// https://llvm.org/bugs/show_bug.cgi?id=25719
+
+float fp_contract_7(float a, float b, float c) {
+// CHECK: _Z13fp_contract_7fff
+// CHECK:  %mul = fmul float %b, 2.000000e+00
+// CHECK-NEXT: fsub float %mul, %c
+  #pragma STDC FP_CONTRACT ON
+  return (a = 2 * b) - c;
+}
+