Fixing a heisenbug where the memory dependence analysis behaves differently

with and without -g.

Adding a test case to make sure that the threshold used in the memory
dependence analysis is respected. The test case also checks that debug
intrinsics are not counted towards this threshold.

Differential Revision: http://llvm-reviews.chandlerc.com/D2141

llvm-svn: 194646

2 files changed, 266 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index fe1c8743a44..84ff2eed12e 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -371,18 +371,19 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
 
   // Walk backwards through the basic block, looking for dependencies.
   while (ScanIt != BB->begin()) {
+    Instruction *Inst = --ScanIt;
+
+    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst))
+      // Debug intrinsics don't (and can't) cause dependencies.
+      if (isa<DbgInfoIntrinsic>(II)) continue;
+
     // Limit the amount of scanning we do so we don't end up with quadratic
     // running time on extreme testcases.
     --Limit;
     if (!Limit)
       return MemDepResult::getUnknown();
 
-    Instruction *Inst = --ScanIt;
-
     if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
-      // Debug intrinsics don't (and can't) cause dependences.
-      if (isa<DbgInfoIntrinsic>(II)) continue;
-
       // If we reach a lifetime begin or end marker, then the query ends here
       // because the value is undefined.
       if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
diff --git a/llvm/test/Transforms/DeadStoreElimination/inst-limits.ll b/llvm/test/Transforms/DeadStoreElimination/inst-limits.ll
new file mode 100644
index 00000000000..1cdf0e1701e
--- /dev/null
+++ b/llvm/test/Transforms/DeadStoreElimination/inst-limits.ll
@@ -0,0 +1,260 @@
+; RUN: opt -S -dse < %s | FileCheck %s
+
+; If there are two stores to the same location, DSE should be able to remove
+; the first store if the two stores are separated by no more than 98
+; instructions. The existence of debug intrinsics between the stores should
+; not affect this instruction limit.
+
+@x = global i32 0, align 4
+
+; Function Attrs: nounwind
+define i32 @test_within_limit() {
+entry:
+  ; The first store; later there is a second store to the same location,
+  ; so this store should be optimized away by DSE.
+  ; CHECK-NOT: store i32 1, i32* @x, align 4
+  store i32 1, i32* @x, align 4
+
+  ; Insert 98 dummy instructions between the two stores
+  %0 = bitcast i32 0 to i32
+  %1 = bitcast i32 0 to i32
+  %2 = bitcast i32 0 to i32
+  %3 = bitcast i32 0 to i32
+  %4 = bitcast i32 0 to i32
+  %5 = bitcast i32 0 to i32
+  %6 = bitcast i32 0 to i32
+  %7 = bitcast i32 0 to i32
+  %8 = bitcast i32 0 to i32
+  %9 = bitcast i32 0 to i32
+  %10 = bitcast i32 0 to i32
+  %11 = bitcast i32 0 to i32
+  %12 = bitcast i32 0 to i32
+  %13 = bitcast i32 0 to i32
+  %14 = bitcast i32 0 to i32
+  %15 = bitcast i32 0 to i32
+  %16 = bitcast i32 0 to i32
+  %17 = bitcast i32 0 to i32
+  %18 = bitcast i32 0 to i32
+  %19 = bitcast i32 0 to i32
+  %20 = bitcast i32 0 to i32
+  %21 = bitcast i32 0 to i32
+  %22 = bitcast i32 0 to i32
+  %23 = bitcast i32 0 to i32
+  %24 = bitcast i32 0 to i32
+  %25 = bitcast i32 0 to i32
+  %26 = bitcast i32 0 to i32
+  %27 = bitcast i32 0 to i32
+  %28 = bitcast i32 0 to i32
+  %29 = bitcast i32 0 to i32
+  %30 = bitcast i32 0 to i32
+  %31 = bitcast i32 0 to i32
+  %32 = bitcast i32 0 to i32
+  %33 = bitcast i32 0 to i32
+  %34 = bitcast i32 0 to i32
+  %35 = bitcast i32 0 to i32
+  %36 = bitcast i32 0 to i32
+  %37 = bitcast i32 0 to i32
+  %38 = bitcast i32 0 to i32
+  %39 = bitcast i32 0 to i32
+  %40 = bitcast i32 0 to i32
+  %41 = bitcast i32 0 to i32
+  %42 = bitcast i32 0 to i32
+  %43 = bitcast i32 0 to i32
+  %44 = bitcast i32 0 to i32
+  %45 = bitcast i32 0 to i32
+  %46 = bitcast i32 0 to i32
+  %47 = bitcast i32 0 to i32
+  %48 = bitcast i32 0 to i32
+  %49 = bitcast i32 0 to i32
+  %50 = bitcast i32 0 to i32
+  %51 = bitcast i32 0 to i32
+  %52 = bitcast i32 0 to i32
+  %53 = bitcast i32 0 to i32
+  %54 = bitcast i32 0 to i32
+  %55 = bitcast i32 0 to i32
+  %56 = bitcast i32 0 to i32
+  %57 = bitcast i32 0 to i32
+  %58 = bitcast i32 0 to i32
+  %59 = bitcast i32 0 to i32
+  %60 = bitcast i32 0 to i32
+  %61 = bitcast i32 0 to i32
+  %62 = bitcast i32 0 to i32
+  %63 = bitcast i32 0 to i32
+  %64 = bitcast i32 0 to i32
+  %65 = bitcast i32 0 to i32
+  %66 = bitcast i32 0 to i32
+  %67 = bitcast i32 0 to i32
+  %68 = bitcast i32 0 to i32
+  %69 = bitcast i32 0 to i32
+  %70 = bitcast i32 0 to i32
+  %71 = bitcast i32 0 to i32
+  %72 = bitcast i32 0 to i32
+  %73 = bitcast i32 0 to i32
+  %74 = bitcast i32 0 to i32
+  %75 = bitcast i32 0 to i32
+  %76 = bitcast i32 0 to i32
+  %77 = bitcast i32 0 to i32
+  %78 = bitcast i32 0 to i32
+  %79 = bitcast i32 0 to i32
+  %80 = bitcast i32 0 to i32
+  %81 = bitcast i32 0 to i32
+  %82 = bitcast i32 0 to i32
+  %83 = bitcast i32 0 to i32
+  %84 = bitcast i32 0 to i32
+  %85 = bitcast i32 0 to i32
+  %86 = bitcast i32 0 to i32
+  %87 = bitcast i32 0 to i32
+  %88 = bitcast i32 0 to i32
+  %89 = bitcast i32 0 to i32
+  %90 = bitcast i32 0 to i32
+  %91 = bitcast i32 0 to i32
+  %92 = bitcast i32 0 to i32
+  %93 = bitcast i32 0 to i32
+  %94 = bitcast i32 0 to i32
+  %95 = bitcast i32 0 to i32
+  %96 = bitcast i32 0 to i32
+  %97 = bitcast i32 0 to i32
+
+  ; Insert a meaningless dbg.value intrinsic; it should have no
+  ; effect on the working of DSE in any way.
+  call void @llvm.dbg.value(metadata !12, i64 0, metadata !10)
+
+  ; CHECK:  store i32 -1, i32* @x, align 4
+  store i32 -1, i32* @x, align 4
+  ret i32 0
+}
+
+; Function Attrs: nounwind
+define i32 @test_outside_limit() {
+entry:
+  ; The first store; later there is a second store to the same location
+  ; CHECK: store i32 1, i32* @x, align 4
+  store i32 1, i32* @x, align 4
+
+  ; Insert 99 dummy instructions between the two stores; this is
+  ; one too many instruction for the DSE to take place.
+  %0 = bitcast i32 0 to i32
+  %1 = bitcast i32 0 to i32
+  %2 = bitcast i32 0 to i32
+  %3 = bitcast i32 0 to i32
+  %4 = bitcast i32 0 to i32
+  %5 = bitcast i32 0 to i32
+  %6 = bitcast i32 0 to i32
+  %7 = bitcast i32 0 to i32
+  %8 = bitcast i32 0 to i32
+  %9 = bitcast i32 0 to i32
+  %10 = bitcast i32 0 to i32
+  %11 = bitcast i32 0 to i32
+  %12 = bitcast i32 0 to i32
+  %13 = bitcast i32 0 to i32
+  %14 = bitcast i32 0 to i32
+  %15 = bitcast i32 0 to i32
+  %16 = bitcast i32 0 to i32
+  %17 = bitcast i32 0 to i32
+  %18 = bitcast i32 0 to i32
+  %19 = bitcast i32 0 to i32
+  %20 = bitcast i32 0 to i32
+  %21 = bitcast i32 0 to i32
+  %22 = bitcast i32 0 to i32
+  %23 = bitcast i32 0 to i32
+  %24 = bitcast i32 0 to i32
+  %25 = bitcast i32 0 to i32
+  %26 = bitcast i32 0 to i32
+  %27 = bitcast i32 0 to i32
+  %28 = bitcast i32 0 to i32
+  %29 = bitcast i32 0 to i32
+  %30 = bitcast i32 0 to i32
+  %31 = bitcast i32 0 to i32
+  %32 = bitcast i32 0 to i32
+  %33 = bitcast i32 0 to i32
+  %34 = bitcast i32 0 to i32
+  %35 = bitcast i32 0 to i32
+  %36 = bitcast i32 0 to i32
+  %37 = bitcast i32 0 to i32
+  %38 = bitcast i32 0 to i32
+  %39 = bitcast i32 0 to i32
+  %40 = bitcast i32 0 to i32
+  %41 = bitcast i32 0 to i32
+  %42 = bitcast i32 0 to i32
+  %43 = bitcast i32 0 to i32
+  %44 = bitcast i32 0 to i32
+  %45 = bitcast i32 0 to i32
+  %46 = bitcast i32 0 to i32
+  %47 = bitcast i32 0 to i32
+  %48 = bitcast i32 0 to i32
+  %49 = bitcast i32 0 to i32
+  %50 = bitcast i32 0 to i32
+  %51 = bitcast i32 0 to i32
+  %52 = bitcast i32 0 to i32
+  %53 = bitcast i32 0 to i32
+  %54 = bitcast i32 0 to i32
+  %55 = bitcast i32 0 to i32
+  %56 = bitcast i32 0 to i32
+  %57 = bitcast i32 0 to i32
+  %58 = bitcast i32 0 to i32
+  %59 = bitcast i32 0 to i32
+  %60 = bitcast i32 0 to i32
+  %61 = bitcast i32 0 to i32
+  %62 = bitcast i32 0 to i32
+  %63 = bitcast i32 0 to i32
+  %64 = bitcast i32 0 to i32
+  %65 = bitcast i32 0 to i32
+  %66 = bitcast i32 0 to i32
+  %67 = bitcast i32 0 to i32
+  %68 = bitcast i32 0 to i32
+  %69 = bitcast i32 0 to i32
+  %70 = bitcast i32 0 to i32
+  %71 = bitcast i32 0 to i32
+  %72 = bitcast i32 0 to i32
+  %73 = bitcast i32 0 to i32
+  %74 = bitcast i32 0 to i32
+  %75 = bitcast i32 0 to i32
+  %76 = bitcast i32 0 to i32
+  %77 = bitcast i32 0 to i32
+  %78 = bitcast i32 0 to i32
+  %79 = bitcast i32 0 to i32
+  %80 = bitcast i32 0 to i32
+  %81 = bitcast i32 0 to i32
+  %82 = bitcast i32 0 to i32
+  %83 = bitcast i32 0 to i32
+  %84 = bitcast i32 0 to i32
+  %85 = bitcast i32 0 to i32
+  %86 = bitcast i32 0 to i32
+  %87 = bitcast i32 0 to i32
+  %88 = bitcast i32 0 to i32
+  %89 = bitcast i32 0 to i32
+  %90 = bitcast i32 0 to i32
+  %91 = bitcast i32 0 to i32
+  %92 = bitcast i32 0 to i32
+  %93 = bitcast i32 0 to i32
+  %94 = bitcast i32 0 to i32
+  %95 = bitcast i32 0 to i32
+  %96 = bitcast i32 0 to i32
+  %97 = bitcast i32 0 to i32
+  %98 = bitcast i32 0 to i32
+
+  ; CHECK:  store i32 -1, i32* @x, align 4
+  store i32 -1, i32* @x, align 4
+  ret i32 0
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!11}
+
+!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.4", i1 true, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !9, metadata !2, metadata !""} ; [ DW_TAG_compile_unit ] [/home/tmp/test.c] [DW_LANG_C99]
+!1 = metadata !{metadata !"test.c", metadata !"/home/tmp"}
+!2 = metadata !{i32 0}
+!3 = metadata !{metadata !4}
+!4 = metadata !{i32 786478, metadata !1, metadata !5, metadata !"test_within_limit", metadata !"test_within_limit", metadata !"", i32 3, metadata !6, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 false, i32 ()* @test_within_limit, null, null, metadata !2, i32 4} ; [ DW_TAG_subprogram ] [line 3] [def] [scope 4] [test]
+!5 = metadata !{i32 786473, metadata !1}          ; [ DW_TAG_file_type ] [/home/tmp/test.c]
+!6 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !7, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!7 = metadata !{metadata !8}
+!8 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!9 = metadata !{metadata !10}
+!10 = metadata !{i32 786484, i32 0, null, metadata !"x", metadata !"x", metadata !"", metadata !5, i32 1, metadata !8, i32 0, i32 1, i32* @x, null} ; [ DW_TAG_variable ] [x] [line 1] [def]
+!11 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
+!12 = metadata !{i32* undef}
+