[llvm-commits] [llvm] r83794 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/mul.ll

[Chris Lattner]

Author: lattner
Date: Sun Oct 11 16:29:45 2009
New Revision: 83794

URL: http://llvm.org/viewvc/llvm-project?rev=83794&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
    llvm/trunk/test/Transforms/InstCombine/mul.ll

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=83794&r1=83793&r2=83794&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Sun Oct 11 16:29:45 2009
@@ -2781,20 +2781,18 @@
   
   // 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);

Modified: llvm/trunk/test/Transforms/InstCombine/mul.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/mul.ll?rev=83794&r1=83793&r2=83794&view=diff

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/mul.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/mul.ll Sun Oct 11 16:29:45 2009
@@ -105,5 +105,12 @@
         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
+}
+