[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286969 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index ce37e3b3da6e9ed4fc78fa21a27d1d7dc1798649..d17039598136648817db81dc7d4082d2b935cf31 100644 (file)
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6469,15 +6469,16 @@ LoopVectorizationCostModel::calculateRegisterUsage(ArrayRef<unsigned> VFs) {
 
   for (unsigned int i = 0; i < Index; ++i) {
     Instruction *I = IdxToInstr[i];
-    // Ignore instructions that are never used within the loop.
-    if (!Ends.count(I))
-      continue;
 
     // Remove all of the instructions that end at this location.
     InstrList &List = TransposeEnds[i];
     for (Instruction *ToRemove : List)
       OpenIntervals.erase(ToRemove);
 
+    // Ignore instructions that are never used within the loop.
+    if (!Ends.count(I))
+      continue;
+
     // Skip ignored values.
     if (ValuesToIgnore.count(I))
       continue;

diff --git a/test/Transforms/LoopVectorize/X86/reg-usage-debug.ll b/test/Transforms/LoopVectorize/X86/reg-usage-debug.ll
new file mode 100644 (file)
index 0000000..d65dd9d
--- /dev/null
+++ b/test/Transforms/LoopVectorize/X86/reg-usage-debug.ll
@@ -0,0 +1,134 @@
+; RUN: opt < %s -debug-only=loop-vectorize -loop-vectorize -mtriple=x86_64-unknown-linux -S 2>&1 | FileCheck %s
+; REQUIRES: asserts
+
+; Test that the register usage estimation is not affected by the presence of
+; debug intrinsics.
+;
+; In the test below the values %0 and %r.08 are ended in the add instruction
+; preceding the call to the intrinsic, and will be recorded against the index
+; of the call instruction.  This means the debug intrinsic must be considered
+; when erasing instructions from the list of open-intervals.
+;
+; Tests generated from following source (with and without -g):
+
+; unsigned test(unsigned *a, unsigned n) {
+;   unsigned i, r = 0;
+;   for(i = 0; i < n; i++)
+;     r += a[i];
+;   return r;
+; }
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: LV: Checking a loop in "test_g"
+; CHECK: LV(REG): Found max usage: 2
+
+define i32 @test_g(i32* nocapture readonly %a, i32 %n) local_unnamed_addr !dbg !6 {
+entry:
+  tail call void @llvm.dbg.value(metadata i32* %a, i64 0, metadata !12, metadata !16), !dbg !17
+  tail call void @llvm.dbg.value(metadata i32 %n, i64 0, metadata !13, metadata !16), !dbg !18
+  tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !15, metadata !16), !dbg !19
+  tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !14, metadata !16), !dbg !20
+  tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !15, metadata !16), !dbg !19
+  tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !14, metadata !16), !dbg !20
+  %cmp6 = icmp eq i32 %n, 0, !dbg !21
+  br i1 %cmp6, label %for.end, label %for.body.preheader, !dbg !25
+
+for.body.preheader:                               ; preds = %entry
+  %wide.trip.count = zext i32 %n to i64, !dbg !21
+  br label %for.body, !dbg !27
+
+for.body:                                         ; preds = %for.body.preheader, %for.body
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %for.body.preheader ]
+  %r.08 = phi i32 [ %add, %for.body ], [ 0, %for.body.preheader ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv, !dbg !27
+  %0 = load i32, i32* %arrayidx, align 4, !dbg !27, !tbaa !28
+  %add = add i32 %0, %r.08, !dbg !32
+  tail call void @llvm.dbg.value(metadata i32 %add, i64 0, metadata !15, metadata !16), !dbg !19
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1, !dbg !33
+  tail call void @llvm.dbg.value(metadata i32 %add, i64 0, metadata !15, metadata !16), !dbg !19
+  %exitcond = icmp eq i64 %indvars.iv.next, %wide.trip.count, !dbg !21
+  br i1 %exitcond, label %for.end.loopexit, label %for.body, !dbg !25, !llvm.loop !35
+
+for.end.loopexit:                                 ; preds = %for.body
+  br label %for.end, !dbg !38
+
+for.end:                                          ; preds = %for.end.loopexit, %entry
+  %r.0.lcssa = phi i32 [ 0, %entry ], [ %add, %for.end.loopexit ]
+  ret i32 %r.0.lcssa, !dbg !38
+}
+
+; CHECK: LV: Checking a loop in "test"
+; CHECK: LV(REG): Found max usage: 2
+
+define i32 @test(i32* nocapture readonly %a, i32 %n) local_unnamed_addr {
+entry:
+  %cmp6 = icmp eq i32 %n, 0
+  br i1 %cmp6, label %for.end, label %for.body.preheader
+
+for.body.preheader:                               ; preds = %entry
+  %wide.trip.count = zext i32 %n to i64
+  br label %for.body
+
+for.body:                                         ; preds = %for.body.preheader, %for.body
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %for.body.preheader ]
+  %r.08 = phi i32 [ %add, %for.body ], [ 0, %for.body.preheader ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4, !tbaa !28
+  %add = add i32 %0, %r.08
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp eq i64 %indvars.iv.next, %wide.trip.count
+  br i1 %exitcond, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:                                 ; preds = %for.body
+  br label %for.end
+
+for.end:                                          ; preds = %for.end.loopexit, %entry
+  %r.0.lcssa = phi i32 [ 0, %entry ], [ %add, %for.end.loopexit ]
+  ret i32 %r.0.lcssa
+}
+
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!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)
+!7 = !DISubroutineType(types: !8)
+!8 = !{!9, !10, !9}
+!9 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64)
+!11 = !{!12, !13, !14, !15}
+!12 = !DILocalVariable(name: "a", arg: 1, scope: !6, file: !1, line: 1, type: !10)
+!13 = !DILocalVariable(name: "n", arg: 2, scope: !6, file: !1, line: 1, type: !9)
+!14 = !DILocalVariable(name: "i", scope: !6, file: !1, line: 2, type: !9)
+!15 = !DILocalVariable(name: "r", scope: !6, file: !1, line: 2, type: !9)
+!16 = !DIExpression()
+!17 = !DILocation(line: 1, column: 27, scope: !6)
+!18 = !DILocation(line: 1, column: 39, scope: !6)
+!19 = !DILocation(line: 2, column: 15, scope: !6)
+!20 = !DILocation(line: 2, column: 12, scope: !6)
+!21 = !DILocation(line: 3, column: 16, scope: !22)
+!22 = !DILexicalBlockFile(scope: !23, file: !1, discriminator: 1)
+!23 = distinct !DILexicalBlock(scope: !24, file: !1, line: 3, column: 3)
+!24 = distinct !DILexicalBlock(scope: !6, file: !1, line: 3, column: 3)
+!25 = !DILocation(line: 3, column: 3, scope: !26)
+!26 = !DILexicalBlockFile(scope: !24, file: !1, discriminator: 1)
+!27 = !DILocation(line: 4, column: 10, scope: !23)
+!28 = !{!29, !29, i64 0}
+!29 = !{!"int", !30, i64 0}
+!30 = !{!"omnipotent char", !31, i64 0}
+!31 = !{!"Simple C/C++ TBAA"}
+!32 = !DILocation(line: 4, column: 7, scope: !23)
+!33 = !DILocation(line: 3, column: 22, scope: !34)
+!34 = !DILexicalBlockFile(scope: !23, file: !1, discriminator: 2)
+!35 = distinct !{!35, !36, !37}
+!36 = !DILocation(line: 3, column: 3, scope: !24)
+!37 = !DILocation(line: 4, column: 13, scope: !24)
+!38 = !DILocation(line: 5, column: 3, scope: !6)

diff --git a/test/Transforms/LoopVectorize/X86/reg-usage.ll b/test/Transforms/LoopVectorize/X86/reg-usage.ll
index 6133635a8ad08f10457d79b1074c69b4fbf86f9b..83974d2db80982f9e36f36bcc9ad7b67a84e055a 100644 (file)
--- a/test/Transforms/LoopVectorize/X86/reg-usage.ll
+++ b/test/Transforms/LoopVectorize/X86/reg-usage.ll
@@ -85,7 +85,7 @@ for.body:                                         ; preds = %for.body, %entry
 define i64 @bar(i64* nocapture %a) {
 ; CHECK-LABEL: bar
 ; CHECK:       LV(REG): VF = 2
-; CHECK:       LV(REG): Found max usage: 4
+; CHECK:       LV(REG): Found max usage: 3
 ;
 entry:
   br label %for.body