[PATCH] D80034: [Local] Do not ignore zexts in salvageDebugInfo, PR45923

[Vedant Kumar via Phabricator via llvm-commits]

vsk created this revision.
vsk added reviewers: aprantl, jmorse, chrisjackson, davide.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

When salvaging a dead zext instruction, append a convert operation to
the DIExpressions of the debug uses of the instruction, to prevent the
salvaged value from being sign-extended.

I confirmed that lldb prints out the correct unsigned result for "f" in
the example from PR45923 with this changed applied.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D80034

Files:
  llvm/lib/Transforms/Utils/Local.cpp
  llvm/test/Transforms/InstCombine/cast-mul-select.ll


Index: llvm/test/Transforms/InstCombine/cast-mul-select.ll
===================================================================
--- llvm/test/Transforms/InstCombine/cast-mul-select.ll
+++ llvm/test/Transforms/InstCombine/cast-mul-select.ll
@@ -13,8 +13,8 @@
 ; we preserve the debug information in the resulting
 ; instruction.
 ; DBGINFO-LABEL: @mul(
-; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 %x
-; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 %y
+; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 %x, {{.*}} !DIExpression(DW_OP_LLVM_convert, 32, DW_ATE_unsigned, DW_OP_LLVM_convert, 8, DW_ATE_unsigned, DW_OP_stack_value))
+; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 %y, {{.*}} !DIExpression(DW_OP_LLVM_convert, 32, DW_ATE_unsigned, DW_OP_LLVM_convert, 8, DW_ATE_unsigned, DW_OP_stack_value))
 ; DBGINFO-NEXT:    [[C:%.*]] = mul i32 {{.*}}
 ; DBGINFO-NEXT:    [[D:%.*]] = and i32 {{.*}}
 ; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 [[C]]
@@ -175,7 +175,7 @@
 ; Check that we don't drop debug info when a zext is removed.
 define i1 @foo(i1 zeroext %b) {
 ; DBGINFO-LABEL: @foo(
-; DBGINFO-NEXT:  call void @llvm.dbg.value(metadata i1 %b
+; DBGINFO-NEXT:  call void @llvm.dbg.value(metadata i1 %b, {{.*}} !DIExpression(DW_OP_LLVM_convert, 1, DW_ATE_unsigned, DW_OP_LLVM_convert, 8, DW_ATE_unsigned, DW_OP_stack_value))
 ; DBGINFO-NEXT:  ret i1 %b
 
   %frombool = zext i1 %b to i8 
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -1698,13 +1698,14 @@
   };
 
   if (auto *CI = dyn_cast<CastInst>(&I)) {
-    // No-op casts and zexts are irrelevant for debug info.
-    if (CI->isNoopCast(DL) || isa<ZExtInst>(&I))
+    // No-op casts are irrelevant for debug info.
+    if (CI->isNoopCast(DL))
       return SrcDIExpr;
 
     Type *Type = CI->getType();
-    // Casts other than Trunc or SExt to scalar types cannot be salvaged.
-    if (Type->isVectorTy() || (!isa<TruncInst>(&I) && !isa<SExtInst>(&I)))
+    // Casts other than Trunc, SExt, or ZExt to scalar types cannot be salvaged.
+    if (Type->isVectorTy() ||
+        !(isa<TruncInst>(&I) || isa<SExtInst>(&I) || isa<ZExtInst>(&I)))
       return nullptr;
 
     Value *FromValue = CI->getOperand(0);


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