[PATCH] D131487: [TypePromotion] Don't insert Truncate for a no-op ZExt

[Andre Vieira via Phabricator via llvm-commits]

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Hi,

As the title says, I don't believe there's a point in inserting Truncates before ZExt's that have no-effect, i.e. ZExts where the argument's type width is the same as the result's type width.

This is a prerequisite for the test in D111237 <https://reviews.llvm.org/D111237> to pass.


https://reviews.llvm.org/D131487

Files:
  llvm/lib/CodeGen/TypePromotion.cpp
  llvm/test/Transforms/TypePromotion/AArch64/phi-zext-gep.ll


Index: llvm/test/Transforms/TypePromotion/AArch64/phi-zext-gep.ll
===================================================================
--- llvm/test/Transforms/TypePromotion/AArch64/phi-zext-gep.ll
+++ llvm/test/Transforms/TypePromotion/AArch64/phi-zext-gep.ll
@@ -24,7 +24,6 @@
 ; CHECK-NEXT:    br label [[FOR_END]]
 ; CHECK:       for.end:
 ; CHECK-NEXT:    [[TAG_0_IN_LCSSA:%.*]] = phi i32 [ [[TMP0]], [[ENTRY:%.*]] ], [ [[TMP1]], [[FOR_END_LOOPEXIT]] ]
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i32 [[TAG_0_IN_LCSSA]] to i8
 ; CHECK-NEXT:    ret i32 [[TAG_0_IN_LCSSA]]
 ;
 entry:
Index: llvm/lib/CodeGen/TypePromotion.cpp
===================================================================
--- llvm/lib/CodeGen/TypePromotion.cpp
+++ llvm/lib/CodeGen/TypePromotion.cpp
@@ -551,8 +551,11 @@
     }
 
     // Don't insert a trunc for a zext which can still legally promote.
+    // Nor insert a trunc for a zext with the same input type as output, this
+    // was a zext that was part of a promotion mutation and will be removed
+    // after.
     if (auto ZExt = dyn_cast<ZExtInst>(I))
-      if (ZExt->getType()->getScalarSizeInBits() > PromotedWidth)
+      if (ZExt->getType()->getScalarSizeInBits() >= PromotedWidth)
         continue;
 
     // Now handle the others.


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