[IndVarSimplify][Dwarf] When widening the IV increment, correctly set the debug loc.

When indvars widened an induction variable, the debug location for the loop
increment computation was incorrectly set equal to the debug loc of the loop
latch terminator.

This patch fixes the issue by propagating the correct location from the
original loop increment instruction to the new widened increment.

Differential Revision: https://reviews.llvm.org/D25872

llvm-svn: 285083

2 files changed, 88 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 5bd1808ac7c..ab1076582f0 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1552,6 +1552,11 @@ PHINode *WidenIV::createWideIV(SCEVExpander &Rewriter) {
     WideInc =
       cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
     WideIncExpr = SE->getSCEV(WideInc);
+    // Propagate the debug location associated with the original loop increment
+    // to the new (widened) increment.
+    auto *OrigInc =
+      cast<Instruction>(OrigPhi->getIncomingValueForBlock(LatchBlock));
+    WideInc->setDebugLoc(OrigInc->getDebugLoc());
   }
 
   DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n");
diff --git a/llvm/test/DebugInfo/Generic/indvar-discriminator.ll b/llvm/test/DebugInfo/Generic/indvar-discriminator.ll
new file mode 100644
index 00000000000..1cd47ebbe38
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/indvar-discriminator.ll
@@ -0,0 +1,83 @@
+; RUN: opt -indvars -S < %s | FileCheck %s
+;
+; When the induction variable is widened by indvars, check that the debug loc
+; associated with the loop increment is correctly propagated.
+;
+; Test case obtained from the following source code:
+;
+; ////
+; extern int foo(int);  // line 1
+;
+; int bar(int X, int *A) {
+;   for (int i = 0; i < X; ++i)  // line 4
+;     A[i] = foo(i);
+;
+;   return A[0];
+; }
+; ///
+;
+; Check that the debug location for the loop increment still refers to
+; line 4, column 26, discriminator 2.
+;
+; CHECK-LABEL: for.body:
+; CHECK: [[PHI:%[0-9a-zA-Z.]+]] = phi i64 [
+; CHECK-LABEL: for.inc:
+; CHECK: add nuw nsw i64 [[PHI]], 1, !dbg ![[INDVARMD:[0-9]+]]
+; CHECK-DAG: ![[INDVARMD]] = !DILocation(line: 4, column: 26, scope: ![[INDVARSCOPEMD:[0-9]+]])
+; CHECK-DAG: ![[INDVARSCOPEMD]] = !DILexicalBlockFile(scope: !{{[0-9]+}}, file: !{{[0-9]+}}, discriminator: 2)
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+define i32 @bar(i32 %X, i32* %A) !dbg !5 {
+entry:
+  %cmp5 = icmp sgt i32 %X, 0, !dbg !7
+  br i1 %cmp5, label %for.body.lr.ph, label %for.end, !dbg !9
+
+for.body.lr.ph:
+  br label %for.body, !dbg !9
+
+for.body:
+  %i.06 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.inc ]
+  %call = call i32 @foo(i32 %i.06), !dbg !10
+  %idxprom = sext i32 %i.06 to i64, !dbg !11
+  %arrayidx = getelementptr inbounds i32, i32* %A, i64 %idxprom, !dbg !11
+  store i32 %call, i32* %arrayidx, align 4, !dbg !12
+  br label %for.inc, !dbg !11
+
+for.inc:
+  %inc = add nsw i32 %i.06, 1, !dbg !13
+  %cmp = icmp slt i32 %inc, %X, !dbg !7
+  br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge, !dbg !9, !llvm.loop !15
+
+for.cond.for.end_crit_edge:
+  br label %for.end, !dbg !9
+
+for.end:
+  %0 = load i32, i32* %A, align 4, !dbg !17
+  ret i32 %0, !dbg !18
+}
+
+declare i32 @foo(i32)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "", isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 3, type: !6, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!6 = !DISubroutineType(types: !2)
+!7 = !DILocation(line: 4, column: 21, scope: !8)
+!8 = !DILexicalBlockFile(scope: !5, file: !1, discriminator: 1)
+!9 = !DILocation(line: 4, column: 3, scope: !8)
+!10 = !DILocation(line: 5, column: 12, scope: !5)
+!11 = !DILocation(line: 5, column: 5, scope: !5)
+!12 = !DILocation(line: 5, column: 10, scope: !5)
+!13 = !DILocation(line: 4, column: 26, scope: !14)
+!14 = !DILexicalBlockFile(scope: !5, file: !1, discriminator: 2)
+!15 = distinct !{!15, !16}
+!16 = !DILocation(line: 4, column: 3, scope: !5)
+!17 = !DILocation(line: 7, column: 10, scope: !5)
+!18 = !DILocation(line: 7, column: 3, scope: !5)