Teach ValueTracking a new way to analyze PHI nodes, and and teach
Instcombine to be more aggressive about using SimplifyDemandedBits
on shift nodes. This allows a shift to be simplified to zero in the
included test case.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72204 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 527ed43..df5145d 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -7152,6 +7152,10 @@
return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
}
+ // See if we can fold away this shift.
+ if (!isa<VectorType>(I.getType()) && SimplifyDemandedInstructionBits(I))
+ return &I;
+
// Try to fold constant and into select arguments.
if (isa<Constant>(Op0))
if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
@@ -7171,8 +7175,6 @@
// See if we can simplify any instructions used by the instruction whose sole
// purpose is to compute bits we don't care about.
uint32_t TypeBits = Op0->getType()->getPrimitiveSizeInBits();
- if (SimplifyDemandedInstructionBits(I))
- return &I;
// shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr
// of a signed value.