[llvm] r336254 - [DebugInfo][InstCombine] Preserve DI after combining zext

[Anastasis Grammenos via llvm-commits]

Author: gramanas
Date: Wed Jul  4 02:55:46 2018
New Revision: 336254

URL: http://llvm.org/viewvc/llvm-project?rev=336254&view=rev
Log:
[DebugInfo][InstCombine] Preserve DI after combining zext

When zext is EvaluatedInDifferentType, InstCombine
drops the dbg.value intrinsic. This patch tries to
preserve said DI, by inserting the zext's old DI in the
resulting instruction. (Only for integer type for now)

Differential Revision: https://reviews.llvm.org/D48331

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
    llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=336254&r1=336253&r2=336254&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Wed Jul  4 02:55:46 2018
@@ -1079,6 +1079,17 @@ Instruction *InstCombiner::visitZExt(ZEx
     Value *Res = EvaluateInDifferentType(Src, DestTy, false);
     assert(Res->getType() == DestTy);
 
+    // When DestTy is integer, try to preserve any debug values referring
+    // to the zext being replaced.
+    // TODO: This should work for vectors as well, possibly via the use
+    // of DWARF fragments.
+    if (DestTy->isIntegerTy()) {
+      insertReplacementDbgValues(
+          *Src, *Res, CI, [](DbgInfoIntrinsic &OldDII) -> DIExpression * {
+            return OldDII.getExpression();
+          });
+    }
+
     uint32_t SrcBitsKept = SrcTy->getScalarSizeInBits()-BitsToClear;
     uint32_t DestBitSize = DestTy->getScalarSizeInBits();
 

Modified: llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll?rev=336254&r1=336253&r2=336254&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll Wed Jul  4 02:55:46 2018
@@ -1,5 +1,5 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -instcombine -S | FileCheck %s
+; RUN: opt -debugify -instcombine -S < %s | FileCheck %s -check-prefix DBGINFO
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32"
 
@@ -8,7 +8,16 @@ define i32 @mul(i32 %x, i32 %y) {
 ; CHECK-NEXT:    [[C:%.*]] = mul i32 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    [[D:%.*]] = and i32 [[C]], 255
 ; CHECK-NEXT:    ret i32 [[D]]
-;
+
+; Test that when zext is evaluated in different type
+; we preserve the debug information in the resulting
+; instruction.
+; DBGINFO-LABEL: @mul(
+; DBGINFO-NEXT:    [[C:%.*]] = mul i32 {{.*}}
+; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 [[C]]
+; DBGINFO-NEXT:    [[D:%.*]] = and i32 {{.*}}
+; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 [[D]]
+
   %A = trunc i32 %x to i8
   %B = trunc i32 %y to i8
   %C = mul i8 %A, %B