[LoopStrengthReduce] Ensure that debug intrinsics do not affect LSR's output

During Loop Strength Reduce, if the terminating condition for the loop
is not immediately adjacent to the terminating branch and it has more
than one use, a clone of the condition will be created just before the
terminating branch and will be used as the branch condition. Currently,
whether the instructions are "immediately adjacent" is determined by
checking whether the next instruction after the condition is the
terminating branch; this is incorrect however, as the presence of a
debug intrinsic between the two will result in a change to the output.
This is fixed by using getNextNonDebugInstruction() instead.

Differential Revision: https://reviews.llvm.org/D103033

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 2fe733e..5fdc5a7 100644 (file)
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -2477,7 +2477,7 @@ LSRInstance::OptimizeLoopTermCond() {
     // It's possible for the setcc instruction to be anywhere in the loop, and
     // possible for it to have multiple users.  If it is not immediately before
     // the exiting block branch, move it.
-    if (&*++BasicBlock::iterator(Cond) != TermBr) {
+    if (Cond->getNextNonDebugInstruction() != TermBr) {
       if (Cond->hasOneUse()) {
         Cond->moveBefore(TermBr);
       } else {

diff --git a/llvm/test/Transforms/LoopStrengthReduce/X86/lsr-cond-dbg.ll b/llvm/test/Transforms/LoopStrengthReduce/X86/lsr-cond-dbg.ll
new file mode 100644 (file)
index 0000000..4b30c00
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/X86/lsr-cond-dbg.ll
@@ -0,0 +1,93 @@
+; RUN: opt -S -loop-reduce < %s | FileCheck %s
+
+; During Loop Strength Reduce, if the terminating condition for the loop is not
+; immediately adjacent to the terminating branch and it has more than one use,
+; a clone of the condition will be created just before the terminating branch
+; and will be used as the branch condition.
+; The purpose of this test is to check that the presence of a debug intrinsic
+; between the condition and branch does not trigger this behaviour, as this
+; would cause debug info to affect CodeGen.
+
+; CHECK-LABEL: i:
+; CHECK-NOT: icmp
+; CHECK: [[COND:%.*]] = icmp eq i8
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i1 [[COND]]
+; CHECK-NEXT: br i1 [[COND]]
+
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@b = dso_local local_unnamed_addr global i8 0, align 1, !dbg !0
+@a = dso_local local_unnamed_addr global i32 0, align 4, !dbg !6
+@c = dso_local local_unnamed_addr global i8 0, align 1, !dbg !9
+define dso_local signext i16 @d() local_unnamed_addr !dbg !17 {
+entry:
+  %0 = load i32, i32* @a, align 4
+  %tobool2.not = icmp eq i32 %0, 0
+  %1 = load i8, i8* @b, align 1, !dbg !24
+  %cmp.not13 = icmp eq i8 %1, 7, !dbg !24
+  br i1 %cmp.not13, label %cleanup, label %if.end.preheader, !dbg !24
+
+if.end.preheader:                                 ; preds = %entry
+  br label %if.end, !dbg !24
+
+if.end:                                           ; preds = %if.end.preheader, %i
+  %2 = phi i8 [ %add, %i ], [ %1, %if.end.preheader ]
+  br i1 %tobool2.not, label %i, label %if.end4, !dbg !24
+
+if.end4:                                          ; preds = %if.end
+  %conv5 = trunc i32 %0 to i16, !dbg !24
+  br label %cleanup, !dbg !24
+
+i:                                                ; preds = %if.end
+  %add = add i8 %2, 1, !dbg !24
+  store i8 %add, i8* @b, align 1, !dbg !24
+  %cmp.not = icmp eq i8 %add, 7, !dbg !24
+  call void @llvm.dbg.value(metadata i1 %cmp.not, metadata !23, metadata !DIExpression(DW_OP_LLVM_convert, 1, DW_ATE_unsigned, DW_OP_LLVM_convert, 32, DW_ATE_unsigned, DW_OP_stack_value)), !dbg !24
+  br i1 %cmp.not, label %cleanup.loopexit, label %if.end, !dbg !24
+
+cleanup.loopexit:                                 ; preds = %i
+  br label %cleanup
+
+cleanup:                                          ; preds = %cleanup.loopexit, %if.end4, %entry
+  %cmp.not12 = phi i1 [ %cmp.not13, %if.end4 ], [ %cmp.not13, %entry ], [ %cmp.not, %cleanup.loopexit ]
+  %retval.0 = phi i16 [ %conv5, %if.end4 ], [ undef, %entry ], [ undef, %cleanup.loopexit ]
+  %3 = load i8, i8* @c, align 1
+  %conv8 = sext i8 %3 to i16
+  %retval.1 = select i1 %cmp.not12, i16 %conv8, i16 %retval.0
+  ret i16 %retval.1, !dbg !24
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!12, !13, !14, !15}
+!llvm.ident = !{!16}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "b", scope: !2, file: !3, line: 2, type: !11, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 13.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "lsr-cond-dbg.c", directory: "/")
+!4 = !{}
+!5 = !{!6, !0, !9}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "a", scope: !2, file: !3, line: 1, type: !8, isLocal: false, isDefinition: true)
+!8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!9 = !DIGlobalVariableExpression(var: !10, expr: !DIExpression())
+!10 = distinct !DIGlobalVariable(name: "c", scope: !2, file: !3, line: 2, type: !11, isLocal: false, isDefinition: true)
+!11 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!12 = !{i32 7, !"Dwarf Version", i32 4}
+!13 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !{i32 1, !"wchar_size", i32 4}
+!15 = !{i32 7, !"uwtable", i32 1}
+!16 = !{!"clang version 13.0.0"}
+!17 = distinct !DISubprogram(name: "d", scope: !3, file: !3, line: 3, type: !18, scopeLine: 3, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !21)
+!18 = !DISubroutineType(types: !19)
+!19 = !{!20}
+!20 = !DIBasicType(name: "short", size: 16, encoding: DW_ATE_signed)
+!21 = !{!23}
+!22 = distinct !DILexicalBlock(scope: !17, file: !3, line: 4, column: 3)
+!23 = !DILocalVariable(name: "g", scope: !22, file: !3, line: 7, type: !8)
+!24 = !DILocation(line: 5, column: 9, scope: !22)
+