[InstCombine] Preserve debug values for eliminable casts
A cast from A to B is eliminable if its result is casted to C, and if
the pair of casts could just be expressed as a single cast. E.g here,
%c1 is eliminable:
%c1 = zext i16 %A to i32
%c2 = sext i32 %c1 to i64
InstCombine optimizes away eliminable casts. This patch teaches it to
insert a dbg.value intrinsic pointing to the final result, so that local
variables pointing to the eliminable result are preserved.
Differential Revision: https://reviews.llvm.org/D42566
llvm-svn: 323570
diff --git a/llvm/test/Transforms/InstCombine/debuginfo-variables.ll b/llvm/test/Transforms/InstCombine/debuginfo-variables.ll
new file mode 100644
index 0000000..c3cd79b
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/debuginfo-variables.ll
@@ -0,0 +1,18 @@
+; RUN: opt < %s -debugify -instcombine -S | FileCheck %s
+
+define i64 @test_sext_zext(i16 %A) {
+; CHECK-LABEL: @test_sext_zext(
+; CHECK-NEXT: [[C2:%.*]] = zext i16 %A to i64
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i64 [[C2]], metadata !8, metadata !DIExpression()), !dbg !13
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i64 [[C2]], metadata !10, metadata !DIExpression()), !dbg !12
+ %c1 = zext i16 %A to i32
+ %c2 = sext i32 %c1 to i64
+ ret i64 %c2
+}
+
+; CHECK: !8 = !DILocalVariable(name: "1", scope: !5, file: !1, line: 1, type: !9)
+; CHECK: !9 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+; CHECK: !10 = !DILocalVariable(name: "2", scope: !5, file: !1, line: 2, type: !11)
+; CHECK: !11 = !DIBasicType(name: "ty64", size: 64, encoding: DW_ATE_unsigned)
+; CHECK: !12 = !DILocation(line: 2, column: 1, scope: !5)
+; CHECK: !13 = !DILocation(line: 1, column: 1, scope: !5)