[llvm] f81200a - [InstCombine] add one-use check to add+xor transform

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2020-10-11T09:04:24-04:00
New Revision: f81200ae9959e0b0c66a2191f30afb8dd5bf7afa

URL: https://github.com/llvm/llvm-project/commit/f81200ae9959e0b0c66a2191f30afb8dd5bf7afa
DIFF: https://github.com/llvm/llvm-project/commit/f81200ae9959e0b0c66a2191f30afb8dd5bf7afa.diff

LOG: [InstCombine] add one-use check to add+xor transform

As shown in the affected test, we could increase instruction
count without this limitation. There's another test with extra
use that shows we still convert directly to a real "sext" if
possible.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    llvm/test/Transforms/InstCombine/signext.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 7fc472de5790..2dd5180378a1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1290,7 +1290,7 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
   Type *Ty = I.getType();
   if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
     Value *XorLHS = nullptr; ConstantInt *XorRHS = nullptr;
-    if (match(LHS, m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS)))) {
+    if (match(LHS, m_OneUse(m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS))))) {
       unsigned TySizeBits = Ty->getScalarSizeInBits();
       const APInt &RHSVal = CI->getValue();
       unsigned ExtendAmt = 0;

diff  --git a/llvm/test/Transforms/InstCombine/signext.ll b/llvm/test/Transforms/InstCombine/signext.ll
index 64eea3ee55e3..4faf4e384874 100644
--- a/llvm/test/Transforms/InstCombine/signext.ll
+++ b/llvm/test/Transforms/InstCombine/signext.ll
@@ -22,8 +22,7 @@ define i32 @sextinreg_extra_use(i32 %x) {
 ; CHECK-NEXT:    [[T1:%.*]] = and i32 [[X:%.*]], 65535
 ; CHECK-NEXT:    [[T2:%.*]] = xor i32 [[T1]], -32768
 ; CHECK-NEXT:    call void @use(i32 [[T2]])
-; CHECK-NEXT:    [[SEXT:%.*]] = shl i32 [[X]], 16
-; CHECK-NEXT:    [[T3:%.*]] = ashr exact i32 [[SEXT]], 16
+; CHECK-NEXT:    [[T3:%.*]] = add nsw i32 [[T2]], 32768
 ; CHECK-NEXT:    ret i32 [[T3]]
 ;
   %t1 = and i32 %x, 65535