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Phi speculation improvement for BasicAA

This is a partial solution to PR14351. It removes some of the special
significance of the first incoming phi value in the phi aliasing checking logic
in BasicAA. In the context of a loop, the old logic assumes that the first
incoming value is the interesting one (meaning that it is the one that comes
from outside the loop), but this is often not the case.  With this change, we
now test first the incoming value that comes from a block other than the parent
of the phi being tested.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168245 91177308-0d34-0410-b5e6-96231b3b80d8
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1 parent 976d440 commit 5c7121e81318b9fde28fe84a2aeb87b162316d9b @hfinkel hfinkel committed Nov 17, 2012
Showing with 83 additions and 3 deletions.
  1. +12 −3 lib/Analysis/BasicAliasAnalysis.cpp
  2. +71 −0 test/Analysis/BasicAA/phi-spec-order.ll
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15 lib/Analysis/BasicAliasAnalysis.cpp
@@ -1065,9 +1065,15 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
if (PN > V2)
std::swap(Locs.first, Locs.second);
+ // Find the first incoming phi value not from its parent.
+ unsigned f = 0;
+ while (PN->getIncomingBlock(f) == PN->getParent() &&
+ f < PN->getNumIncomingValues()-1)
+ ++f;
+
AliasResult Alias =
- aliasCheck(PN->getIncomingValue(0), PNSize, PNTBAAInfo,
- PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)),
+ aliasCheck(PN->getIncomingValue(f), PNSize, PNTBAAInfo,
+ PN2->getIncomingValueForBlock(PN->getIncomingBlock(f)),
V2Size, V2TBAAInfo);
if (Alias == MayAlias)
return MayAlias;
@@ -1096,7 +1102,10 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
ArePhisAssumedNoAlias = true;
}
- for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ if (i == f)
+ continue;
+
AliasResult ThisAlias =
aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
View
71 test/Analysis/BasicAA/phi-spec-order.ll
@@ -0,0 +1,71 @@
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
+target triple = "powerpc64-bgq-linux"
+; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
+
+@X = external global [16000 x double], align 32
+@Y = external global [16000 x double], align 32
+
+define signext i32 @s000() nounwind {
+entry:
+ br label %for.cond2.preheader
+
+for.cond2.preheader: ; preds = %for.end, %entry
+ %nl.018 = phi i32 [ 0, %entry ], [ %inc9, %for.end ]
+ br label %for.body4
+
+for.body4: ; preds = %for.body4, %for.cond2.preheader
+ %lsr.iv4 = phi [16000 x double]* [ %i11, %for.body4 ], [ bitcast (double* getelementptr inbounds ([16000 x double]* @Y, i64 0, i64 8)
+ to [16000 x double]*), %for.cond2.preheader ]
+ %lsr.iv1 = phi [16000 x double]* [ %i10, %for.body4 ], [ @X, %for.cond2.preheader ]
+
+; CHECK: NoAlias:{{[ \t]+}}[16000 x double]* %lsr.iv1, [16000 x double]* %lsr.iv4
+
+ %lsr.iv = phi i32 [ %lsr.iv.next, %for.body4 ], [ 16000, %for.cond2.preheader ]
+ %lsr.iv46 = bitcast [16000 x double]* %lsr.iv4 to <4 x double>*
+ %lsr.iv12 = bitcast [16000 x double]* %lsr.iv1 to <4 x double>*
+ %scevgep11 = getelementptr <4 x double>* %lsr.iv46, i64 -2
+ %i6 = load <4 x double>* %scevgep11, align 32, !tbaa !0
+ %add = fadd <4 x double> %i6, <double 1.000000e+00, double 1.000000e+00, double 1.000000e+00, double 1.000000e+00>
+ store <4 x double> %add, <4 x double>* %lsr.iv12, align 32, !tbaa !0
+ %scevgep10 = getelementptr <4 x double>* %lsr.iv46, i64 -1
+ %i7 = load <4 x double>* %scevgep10, align 32, !tbaa !0
+ %add.4 = fadd <4 x double> %i7, <double 1.000000e+00, double 1.000000e+00, double 1.000000e+00, double 1.000000e+00>
+ %scevgep9 = getelementptr <4 x double>* %lsr.iv12, i64 1
+ store <4 x double> %add.4, <4 x double>* %scevgep9, align 32, !tbaa !0
+ %i8 = load <4 x double>* %lsr.iv46, align 32, !tbaa !0
+ %add.8 = fadd <4 x double> %i8, <double 1.000000e+00, double 1.000000e+00, double 1.000000e+00, double 1.000000e+00>
+ %scevgep8 = getelementptr <4 x double>* %lsr.iv12, i64 2
+ store <4 x double> %add.8, <4 x double>* %scevgep8, align 32, !tbaa !0
+ %scevgep7 = getelementptr <4 x double>* %lsr.iv46, i64 1
+ %i9 = load <4 x double>* %scevgep7, align 32, !tbaa !0
+ %add.12 = fadd <4 x double> %i9, <double 1.000000e+00, double 1.000000e+00, double 1.000000e+00, double 1.000000e+00>
+ %scevgep3 = getelementptr <4 x double>* %lsr.iv12, i64 3
+ store <4 x double> %add.12, <4 x double>* %scevgep3, align 32, !tbaa !0
+
+; CHECK: NoAlias:{{[ \t]+}}<4 x double>* %scevgep11, <4 x double>* %scevgep7
+; CHECK: NoAlias:{{[ \t]+}}<4 x double>* %scevgep10, <4 x double>* %scevgep7
+; CHECK: NoAlias:{{[ \t]+}}<4 x double>* %scevgep7, <4 x double>* %scevgep9
+; CHECK: NoAlias:{{[ \t]+}}<4 x double>* %scevgep11, <4 x double>* %scevgep3
+; CHECK: NoAlias:{{[ \t]+}}<4 x double>* %scevgep10, <4 x double>* %scevgep3
+; CHECK: NoAlias:{{[ \t]+}}<4 x double>* %scevgep3, <4 x double>* %scevgep9
+
+ %lsr.iv.next = add i32 %lsr.iv, -16
+ %scevgep = getelementptr [16000 x double]* %lsr.iv1, i64 0, i64 16
+ %i10 = bitcast double* %scevgep to [16000 x double]*
+ %scevgep5 = getelementptr [16000 x double]* %lsr.iv4, i64 0, i64 16
+ %i11 = bitcast double* %scevgep5 to [16000 x double]*
+ %exitcond.15 = icmp eq i32 %lsr.iv.next, 0
+ br i1 %exitcond.15, label %for.end, label %for.body4
+
+for.end: ; preds = %for.body4
+ %inc9 = add nsw i32 %nl.018, 1
+ %exitcond = icmp eq i32 %inc9, 400000
+ br i1 %exitcond, label %for.end10, label %for.cond2.preheader
+
+for.end10: ; preds = %for.end
+ ret i32 0
+}
+
+!0 = metadata !{metadata !"double", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA"}

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