[InstSimplify] fold div/rem of zexted bool

I was looking at an unrelated fold and noticed that
we don't have this simplification (because the other
fold would break existing tests).

Name: zext udiv
  %z = zext i1 %x to i32
  %r = udiv i32 %y, %z
=>
  %r = %y

Name: zext urem
  %z = zext i1 %x to i32
  %r = urem i32 %y, %z
=>
  %r = 0

Name: zext sdiv
  %z = zext i1 %x to i32
  %r = sdiv i32 %y, %z
=>
  %r = %y

Name: zext srem
  %z = zext i1 %x to i32
  %r = srem i32 %y, %z
=>
  %r = 0

https://rise4fun.com/Alive/LZ9

llvm-svn: 335512

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index f1bfa33276b..4f5bed91dcc 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -902,7 +902,10 @@ static Value *simplifyDivRem(Value *Op0, Value *Op1, bool IsDiv) {
   // X % 1 -> 0
   // If this is a boolean op (single-bit element type), we can't have
   // division-by-zero or remainder-by-zero, so assume the divisor is 1.
-  if (match(Op1, m_One()) || Ty->isIntOrIntVectorTy(1))
+  // Similarly, if we're zero-extending a boolean divisor, then assume it's a 1.
+  Value *X;
+  if (match(Op1, m_One()) || Ty->isIntOrIntVectorTy(1) ||
+      (match(Op1, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1)))
     return IsDiv ? Op0 : Constant::getNullValue(Ty);
 
   return nullptr;