[PATCH] D125653: [TypePromotion] Fix another case for sext vs zext in promoted constant.

[Craig Topper via Phabricator via llvm-commits]

craig.topper updated this revision to Diff 430879.
craig.topper added a comment.

Use zext for Subtract always.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D125653/new/

https://reviews.llvm.org/D125653

Files:
  llvm/lib/CodeGen/TypePromotion.cpp
  llvm/test/Transforms/TypePromotion/ARM/icmps.ll


Index: llvm/test/Transforms/TypePromotion/ARM/icmps.ll
===================================================================
--- llvm/test/Transforms/TypePromotion/ARM/icmps.ll
+++ llvm/test/Transforms/TypePromotion/ARM/icmps.ll
@@ -361,3 +361,14 @@
   %3 = select i1 %2, i32 1, i32 0
   ret i32 %3
 }
+
+define i1 @pr55490() {
+; CHECK-LABEL: @pr55490(
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i32 10, 8
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ult i32 [[TMP1]], 3
+; CHECK-NEXT:    ret i1 [[TMP2]]
+;
+  %1 = sub i4 -6, -8
+  %2 = icmp ult i4 %1, 3
+  ret i1 %2
+}
Index: llvm/lib/CodeGen/TypePromotion.cpp
===================================================================
--- llvm/lib/CodeGen/TypePromotion.cpp
+++ llvm/lib/CodeGen/TypePromotion.cpp
@@ -484,7 +484,10 @@
         continue;
 
       if (auto *Const = dyn_cast<ConstantInt>(Op)) {
-        Constant *NewConst = (SafeWrap.contains(I) && i == 1)
+        // For subtract, we don't need to sext the constant. We only put it in
+        // SafeWrap because SafeWrap.size() is used elsewhere.
+        Constant *NewConst = (SafeWrap.contains(I) && i == 1 &&
+                              I->getOpcode() != Instruction::Sub)
                                  ? ConstantExpr::getSExt(Const, ExtTy)
                                  : ConstantExpr::getZExt(Const, ExtTy);
         I->setOperand(i, NewConst);


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