[PowerPC] Implement isMaskAndCmp0FoldingBeneficial

Sinking the and closer to a compare against zero is beneficial on PPC as it
allows us to emit record-form instructions. In the future, we may expand this
to a larger set of operations that feed compares against zero since PPC has
lots of record-form instructions.

Differential revision: https://reviews.llvm.org/D46060

llvm-svn: 331416

2 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 83ed349b46f..bea8792a039 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -13978,3 +13978,17 @@ bool PPCTargetLowering::mayBeEmittedAsTailCall(const CallInst *CI) const {
   // If the function is local then we have a good chance at tail-calling it
   return getTargetMachine().shouldAssumeDSOLocal(*Caller->getParent(), Callee);
 }
+
+bool PPCTargetLowering::
+isMaskAndCmp0FoldingBeneficial(const Instruction &AndI) const {
+  const Value *Mask = AndI.getOperand(1);
+  // If the mask is suitable for andi. or andis. we should sink the and.
+  if (const ConstantInt *CI = dyn_cast<ConstantInt>(Mask)) {
+    int64_t ConstVal = CI->getZExtValue();
+    return isUInt<16>(ConstVal) ||
+      (isUInt<16>(ConstVal >> 16) && !(ConstVal & 0xFFFF));
+  }
+
+  // For non-constant masks, we can always use the record-form and.
+  return true;
+}
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index b4373c1dfea..f9d4c20bb2f 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -1101,6 +1101,7 @@ namespace llvm {
     // tail call. This will cause the optimizers to attempt to move, or
     // duplicate return instructions to help enable tail call optimizations.
     bool mayBeEmittedAsTailCall(const CallInst *CI) const override;
+    bool isMaskAndCmp0FoldingBeneficial(const Instruction &AndI) const override;
   }; // end class PPCTargetLowering
 
   namespace PPC {