From: Chris Lattner <sabre@nondot.org>
Date: Sun, 11 Oct 2009 21:29:45 +0000 (+0000)
Subject: generalize a transformation even more: we don't care whether the
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=d2c58366d8d3205f212f026fe373641eebccaebb;p=oota-llvm.git

generalize a transformation even more: we don't care whether the
input the the mul is a zext from bool, just that it is all zeros
other than the low bit.  This fixes some phase ordering issues
that would cause us to miss some xforms in mul.ll when the worklist
is visited differently.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83794 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index e9ffb730305..549c57633a4 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2781,20 +2781,18 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
   
   // If one of the operands of the multiply is a cast from a boolean value, then
   // we know the bool is either zero or one, so this is a 'masking' multiply.
-  // See if we can simplify things based on how the boolean was originally
-  // formed.
-  {
-    Value *BoolCast = 0, *OtherOp = 0;
-    if (ZExtInst *CI = dyn_cast<ZExtInst>(Op0))
-      if (CI->getOperand(0)->getType() == Type::getInt1Ty(*Context))
-        BoolCast = CI, OtherOp = I.getOperand(1);
-    if (!BoolCast)
-      if (ZExtInst *CI = dyn_cast<ZExtInst>(I.getOperand(1)))
-        if (CI->getOperand(0)->getType() == Type::getInt1Ty(*Context))
-          BoolCast = CI, OtherOp = Op0;
+  //   X * Y (where Y is 0 or 1) -> X & (0-Y)
+  if (!isa<VectorType>(I.getType())) {
+    // -2 is "-1 << 1" so it is all bits set except the low one.
+    APInt Negative2(I.getType()->getPrimitiveSizeInBits(), -2, true);
     
+    Value *BoolCast = 0, *OtherOp = 0;
+    if (MaskedValueIsZero(Op0, Negative2))
+      BoolCast = Op0, OtherOp = I.getOperand(1);
+    else if (MaskedValueIsZero(I.getOperand(1), Negative2))
+      BoolCast = I.getOperand(1), OtherOp = Op0;
+
     if (BoolCast) {
-      // X * Y (where Y is 0 or 1) -> X & (0-Y)
       Value *V = Builder->CreateSub(Constant::getNullValue(I.getType()),
                                     BoolCast, "tmp");
       return BinaryOperator::CreateAnd(V, OtherOp);
diff --git a/test/Transforms/InstCombine/mul.ll b/test/Transforms/InstCombine/mul.ll
index d8e623c4834..53a56434aed 100644
--- a/test/Transforms/InstCombine/mul.ll
+++ b/test/Transforms/InstCombine/mul.ll
@@ -105,5 +105,12 @@ define i32 @test16(i32 %b, i1 %c) {
         ret i32 %e
 }
 
+; X * Y (when Y is 0 or 1) --> x & (0-Y)
+define i32 @test17(i32 %a, i32 %b) {
+  %a.lobit = lshr i32 %a, 31
+  %e = mul i32 %a.lobit, %b
+  ret i32 %e
+}
+