Reenable the transform "(X*Y)/Y->X" when the multiplication is known not to

overflow (nsw flag), which was disabled because it breaks 254.gap.  I have
informed the GAP authors of the mistake in their code, and arranged for the
testsuite to use -fwrapv when compiling this benchmark.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124746 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 6ca4dddcf36ae6ce64857e4b3161567a2bbc34e6..4b9b648aa6c10ac3066c1695cc5e41f225f84da6 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -798,11 +798,11 @@ static Value *SimplifyDiv(unsigned Opcode, Value *Op0, Value *Op1,
   Value *X = 0, *Y = 0;
   if (match(Op0, m_Mul(m_Value(X), m_Value(Y))) && (X == Op1 || Y == Op1)) {
     if (Y != Op1) std::swap(X, Y); // Ensure expression is (X * Y) / Y, Y = Op1
-//    BinaryOperator *Mul = cast<BinaryOperator>(Op0);
-//    // If the Mul knows it does not overflow, then we are good to go.
-//    if ((isSigned && Mul->hasNoSignedWrap()) ||
-//        (!isSigned && Mul->hasNoUnsignedWrap()))
-//      return X;
+    BinaryOperator *Mul = cast<BinaryOperator>(Op0);
+    // If the Mul knows it does not overflow, then we are good to go.
+    if ((isSigned && Mul->hasNoSignedWrap()) ||
+        (!isSigned && Mul->hasNoUnsignedWrap()))
+      return X;
     // If X has the form X = A / Y then X * Y cannot overflow.
     if (BinaryOperator *Div = dyn_cast<BinaryOperator>(X))
       if (Div->getOpcode() == Opcode && Div->getOperand(1) == Y)

diff --git a/test/Transforms/InstSimplify/2010-12-20-Reassociate.ll b/test/Transforms/InstSimplify/2010-12-20-Reassociate.ll
index c0ae257dcdc385bff75544c39f8a0646dcc6a015..928442ac56c91c21277136c0bd11d576613e6b0f 100644 (file)
--- a/test/Transforms/InstSimplify/2010-12-20-Reassociate.ll
+++ b/test/Transforms/InstSimplify/2010-12-20-Reassociate.ll
@@ -92,10 +92,12 @@ define i32 @sub3(i32 %x, i32 %y) {
 }
 
 define i32 @sdiv1(i32 %x, i32 %y) {
+; CHECK: @sdiv1
 ; (no overflow X * Y) / Y -> X
   %mul = mul nsw i32 %x, %y
   %r = sdiv i32 %mul, %y
   ret i32 %r
+; CHECK: ret i32 %x
 }
 
 define i32 @sdiv2(i32 %x, i32 %y) {
@@ -136,10 +138,12 @@ define i32 @sdiv5(i32 %x, i32 %y) {
 }
 
 define i32 @udiv1(i32 %x, i32 %y) {
+; CHECK: @udiv1
 ; (no overflow X * Y) / Y -> X
   %mul = mul nuw i32 %x, %y
   %r = udiv i32 %mul, %y
   ret i32 %r
+; CHECK: ret i32 %x
 }
 
 define i32 @udiv2(i32 %x, i32 %y) {