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[LoopVectorizer] When estimating reg usage, unused insts may "end" another use
The register usage algorithm incorrectly treats instructions whose value is not used within the loop (e.g. those that do not produce a value). The algorithm first calculates the usages within the loop. It iterates over the instructions in order, and records at which instruction index each use ends (in fact, they're actually recorded against the next index, as this is when we want to delete them from the open intervals). The algorithm then iterates over the instructions again, adding each instruction in turn to a list of open intervals. Instructions are then removed from the list of open intervals when they occur in the list of uses ended at the current index. The problem is, instructions which are not used in the loop are skipped. However, although they aren't used, the last use of a value may have been recorded against that instruction index. In this case, the use is not deleted from the open intervals, which may then bump up the estimated register usage. This patch fixes the issue by simply moving the "is used" check after the loop which erases the uses at the current index. Differential Revision: https://reviews.llvm.org/D26554 llvm-svn: 286969
This commit is contained in:
Robert Lougher
parent
50bd965fb7
commit
75ef160b89
@ -6469,15 +6469,16 @@ LoopVectorizationCostModel::calculateRegisterUsage(ArrayRef<unsigned> VFs) {
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for (unsigned int i = 0; i < Index; ++i) {
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Instruction *I = IdxToInstr[i];
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// Ignore instructions that are never used within the loop.
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if (!Ends.count(I))
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continue;
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// Remove all of the instructions that end at this location.
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InstrList &List = TransposeEnds[i];
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for (Instruction *ToRemove : List)
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OpenIntervals.erase(ToRemove);
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// Ignore instructions that are never used within the loop.
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if (!Ends.count(I))
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continue;
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// Skip ignored values.
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if (ValuesToIgnore.count(I))
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continue;
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134
test/Transforms/LoopVectorize/X86/reg-usage-debug.ll
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134
test/Transforms/LoopVectorize/X86/reg-usage-debug.ll
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@ -0,0 +1,134 @@
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; RUN: opt < %s -debug-only=loop-vectorize -loop-vectorize -mtriple=x86_64-unknown-linux -S 2>&1 | FileCheck %s
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; REQUIRES: asserts
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; Test that the register usage estimation is not affected by the presence of
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; debug intrinsics.
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;
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; In the test below the values %0 and %r.08 are ended in the add instruction
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; preceding the call to the intrinsic, and will be recorded against the index
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; of the call instruction. This means the debug intrinsic must be considered
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; when erasing instructions from the list of open-intervals.
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;
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; Tests generated from following source (with and without -g):
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; unsigned test(unsigned *a, unsigned n) {
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; unsigned i, r = 0;
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; for(i = 0; i < n; i++)
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; r += a[i];
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; return r;
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; }
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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; CHECK: LV: Checking a loop in "test_g"
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; CHECK: LV(REG): Found max usage: 2
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define i32 @test_g(i32* nocapture readonly %a, i32 %n) local_unnamed_addr !dbg !6 {
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entry:
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tail call void @llvm.dbg.value(metadata i32* %a, i64 0, metadata !12, metadata !16), !dbg !17
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tail call void @llvm.dbg.value(metadata i32 %n, i64 0, metadata !13, metadata !16), !dbg !18
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tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !15, metadata !16), !dbg !19
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tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !14, metadata !16), !dbg !20
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tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !15, metadata !16), !dbg !19
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tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !14, metadata !16), !dbg !20
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%cmp6 = icmp eq i32 %n, 0, !dbg !21
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br i1 %cmp6, label %for.end, label %for.body.preheader, !dbg !25
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for.body.preheader: ; preds = %entry
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%wide.trip.count = zext i32 %n to i64, !dbg !21
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br label %for.body, !dbg !27
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for.body: ; preds = %for.body.preheader, %for.body
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%indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %for.body.preheader ]
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%r.08 = phi i32 [ %add, %for.body ], [ 0, %for.body.preheader ]
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%arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv, !dbg !27
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%0 = load i32, i32* %arrayidx, align 4, !dbg !27, !tbaa !28
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%add = add i32 %0, %r.08, !dbg !32
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tail call void @llvm.dbg.value(metadata i32 %add, i64 0, metadata !15, metadata !16), !dbg !19
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1, !dbg !33
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tail call void @llvm.dbg.value(metadata i32 %add, i64 0, metadata !15, metadata !16), !dbg !19
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%exitcond = icmp eq i64 %indvars.iv.next, %wide.trip.count, !dbg !21
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br i1 %exitcond, label %for.end.loopexit, label %for.body, !dbg !25, !llvm.loop !35
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for.end.loopexit: ; preds = %for.body
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br label %for.end, !dbg !38
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for.end: ; preds = %for.end.loopexit, %entry
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%r.0.lcssa = phi i32 [ 0, %entry ], [ %add, %for.end.loopexit ]
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ret i32 %r.0.lcssa, !dbg !38
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}
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; CHECK: LV: Checking a loop in "test"
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; CHECK: LV(REG): Found max usage: 2
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define i32 @test(i32* nocapture readonly %a, i32 %n) local_unnamed_addr {
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entry:
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%cmp6 = icmp eq i32 %n, 0
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br i1 %cmp6, label %for.end, label %for.body.preheader
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for.body.preheader: ; preds = %entry
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%wide.trip.count = zext i32 %n to i64
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br label %for.body
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for.body: ; preds = %for.body.preheader, %for.body
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%indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %for.body.preheader ]
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%r.08 = phi i32 [ %add, %for.body ], [ 0, %for.body.preheader ]
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%arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
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%0 = load i32, i32* %arrayidx, align 4, !tbaa !28
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%add = add i32 %0, %r.08
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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%exitcond = icmp eq i64 %indvars.iv.next, %wide.trip.count
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br i1 %exitcond, label %for.end.loopexit, label %for.body
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for.end.loopexit: ; preds = %for.body
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br label %for.end
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for.end: ; preds = %for.end.loopexit, %entry
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%r.0.lcssa = phi i32 [ 0, %entry ], [ %add, %for.end.loopexit ]
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ret i32 %r.0.lcssa
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}
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declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!3, !4}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
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!1 = !DIFile(filename: "test.c", directory: "")
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!2 = !{}
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!3 = !{i32 2, !"Dwarf Version", i32 4}
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!4 = !{i32 2, !"Debug Info Version", i32 3}
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!6 = distinct !DISubprogram(name: "test_g", scope: !1, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !11)
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!7 = !DISubroutineType(types: !8)
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!8 = !{!9, !10, !9}
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!9 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
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!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64)
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!11 = !{!12, !13, !14, !15}
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!12 = !DILocalVariable(name: "a", arg: 1, scope: !6, file: !1, line: 1, type: !10)
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!13 = !DILocalVariable(name: "n", arg: 2, scope: !6, file: !1, line: 1, type: !9)
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!14 = !DILocalVariable(name: "i", scope: !6, file: !1, line: 2, type: !9)
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!15 = !DILocalVariable(name: "r", scope: !6, file: !1, line: 2, type: !9)
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!16 = !DIExpression()
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!17 = !DILocation(line: 1, column: 27, scope: !6)
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!18 = !DILocation(line: 1, column: 39, scope: !6)
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!19 = !DILocation(line: 2, column: 15, scope: !6)
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!20 = !DILocation(line: 2, column: 12, scope: !6)
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!21 = !DILocation(line: 3, column: 16, scope: !22)
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!22 = !DILexicalBlockFile(scope: !23, file: !1, discriminator: 1)
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!23 = distinct !DILexicalBlock(scope: !24, file: !1, line: 3, column: 3)
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!24 = distinct !DILexicalBlock(scope: !6, file: !1, line: 3, column: 3)
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!25 = !DILocation(line: 3, column: 3, scope: !26)
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!26 = !DILexicalBlockFile(scope: !24, file: !1, discriminator: 1)
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!27 = !DILocation(line: 4, column: 10, scope: !23)
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!28 = !{!29, !29, i64 0}
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!29 = !{!"int", !30, i64 0}
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!30 = !{!"omnipotent char", !31, i64 0}
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!31 = !{!"Simple C/C++ TBAA"}
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!32 = !DILocation(line: 4, column: 7, scope: !23)
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!33 = !DILocation(line: 3, column: 22, scope: !34)
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!34 = !DILexicalBlockFile(scope: !23, file: !1, discriminator: 2)
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!35 = distinct !{!35, !36, !37}
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!36 = !DILocation(line: 3, column: 3, scope: !24)
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!37 = !DILocation(line: 4, column: 13, scope: !24)
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!38 = !DILocation(line: 5, column: 3, scope: !6)
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@ -85,7 +85,7 @@ for.body: ; preds = %for.body, %entry
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define i64 @bar(i64* nocapture %a) {
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; CHECK-LABEL: bar
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; CHECK: LV(REG): VF = 2
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; CHECK: LV(REG): Found max usage: 4
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; CHECK: LV(REG): Found max usage: 3
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;
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entry:
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br label %for.body
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