forked from OSchip/llvm-project
[EarlyCSEwMemorySSA] Add MSSA verification and tests to make EarlyCSE failures easier to track.
Summary: EarlyCSE can make IR changes that will leave MemorySSA with accesses claiming to be optimized, but for which a subsequent MemorySSA run will yield a different optimized result. Due to relying on AA queries, we can't fix this in general, unless we recompute MemorySSA. Adding some tests to track this and a basic verify for future potential failures. Reviewers: george.burgess.iv, gberry Subscribers: sanjoy, jlebar, Prazek, llvm-commits Differential Revision: https://reviews.llvm.org/D51960 llvm-svn: 342422
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@ -604,6 +604,8 @@ private:
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void removeMSSA(Instruction *Inst) {
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if (!MSSA)
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return;
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if (VerifyMemorySSA)
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MSSA->verifyMemorySSA();
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// Removing a store here can leave MemorySSA in an unoptimized state by
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// creating MemoryPhis that have identical arguments and by creating
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// MemoryUses whose defining access is not an actual clobber. We handle the
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@ -0,0 +1,137 @@
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; RUN: opt < %s -early-cse-memssa -verify-memoryssa -disable-output
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; REQUIRES: asserts
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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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; Tests below highlight scenarios where EarlyCSE does not preserve MemorySSA
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; optimized accesses. Current MemorySSA verify will accept these.
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; Test 1:
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; AA cannot tell here that the last load does not alias the only store.
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; The first two loads are a common expression, EarlyCSE removes the second one,
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; and then AA can see that the last load is a Use(LoE). Hence not optimized as
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; it claims. Note that if we replace the GEP indices 2 and 1, AA sees NoAlias
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; for the last load, before CSE-ing the first 2 loads.
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%struct.ImageParameters = type { i32, i32, i32 }
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@img = external global %struct.ImageParameters*, align 8
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define void @test1_macroblock() {
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entry:
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; MemoryUse(LoE)
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%0 = load %struct.ImageParameters*, %struct.ImageParameters** @img, align 8
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%Pos_2 = getelementptr inbounds %struct.ImageParameters, %struct.ImageParameters* %0, i64 0, i32 2
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; 1 = MemoryDef(LoE)
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store i32 undef, i32* %Pos_2, align 8
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; MemoryUse(LoE)
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%1 = load %struct.ImageParameters*, %struct.ImageParameters** @img, align 8
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%Pos_1 = getelementptr inbounds %struct.ImageParameters, %struct.ImageParameters* %1, i64 0, i32 1
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; MemoryUse(1) MayAlias
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%2 = load i32, i32* %Pos_1, align 4
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unreachable
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}
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; Test 2:
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; EarlyCSE simplifies %string to undef. Def and Use used to be MustAlias, with
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; undef they are NoAlias. The Use can be optimized further to LoE. We can
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; de-optimize uses of replaced instructions, but in general this is not enough
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; (see next tests).
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%struct.TermS = type { i32, i32, i32, i32, i32, i8* }
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define fastcc void @test2_term_string() {
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entry:
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%string = getelementptr inbounds %struct.TermS, %struct.TermS* undef, i64 0, i32 5
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; 1 = MemoryDef(LoE)
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store i8* undef, i8** %string, align 8
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; MemoryUse(1) MustAlias
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%0 = load i8*, i8** %string, align 8
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unreachable
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}
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; Test 3:
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; EarlyCSE simplifies %0 to undef. So the second Def now stores to undef.
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; We now find the second load (Use(2) can be optimized further to LoE)
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; When replacing instructions, we can deoptimize all uses of the replaced
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; instruction and all uses of transitive accesses. However this does not stop
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; MemorySSA from being tripped by AA (see test4).
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%struct.Grammar = type { i8*, i8*, %struct.anon }
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%struct.anon = type { i32, i32, %struct.Term**, [3 x %struct.Term*] }
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%struct.Term = type { i32 }
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define fastcc void @test3_term_string(%struct.Grammar* %g) {
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entry:
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; 1 = MemoryDef(LoE)
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store i8* undef, i8** undef, align 8
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; MemoryUse(LoE)
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%0 = load i8*, i8** undef, align 8
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%arrayidx = getelementptr inbounds i8, i8* %0, i64 undef
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; 2 = MemoryDef(1)
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store i8 0, i8* %arrayidx, align 1
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%v = getelementptr inbounds %struct.Grammar, %struct.Grammar* %g, i64 0, i32 2, i32 2
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; MemoryUse(2) MayAlias
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%1 = load %struct.Term**, %struct.Term*** %v, align 8
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unreachable
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}
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; Test 4:
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; Removing dead/unused instructions in if.then274 makes AA smarter. Before
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; removal, it finds %4 MayAlias the store above. After removal this can be
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; optimized to LoE. Hence after EarlyCSE, there is an access who claims is
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; optimized and it can be optimized further.
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; We can't escape such cases in general when relying on Alias Analysis.
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; The only fail-safe way to actually preserve MemorySSA when removing or
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; replacing instructions (i.e. get the *same* MemorySSA as if it was computed
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; for the updated IR) is to recompute it from scratch. What we get now is still
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; a correct update, but with accesses that claim to be optimized and can be
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; optimized further if we were to re-run MemorySSA on the IR.
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%struct.gnode.0.1.3.6.9.18.20.79 = type { i32, i32, i32, i32, i32, i32, i32, %struct.gnode.0.1.3.6.9.18.20.79* }
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@gnodeArray = external global %struct.gnode.0.1.3.6.9.18.20.79**, align 8
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define void @test4_shortest() {
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entry:
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%exl.i = alloca [5 x i32], align 16
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br i1 undef, label %if.then274, label %for.cond404
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if.then274: ; preds = %if.end256
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%0 = bitcast [5 x i32]* %exl.i to i8*
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%arrayidx.i = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 1
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%arrayidx1.i = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 2
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%arrayidx2.i = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 3
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%arrayidx3.i = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 4
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%1 = bitcast [5 x i32]* %exl.i to i8*
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%arrayidx.i1034 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 1
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%arrayidx1.i1035 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 2
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%arrayidx2.i1036 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 3
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%arrayidx3.i1037 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 4
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unreachable
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for.cond404: ; preds = %if.end256
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%2 = bitcast [5 x i32]* %exl.i to i8*
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%arrayidx.i960 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 1
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%arrayidx1.i961 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 2
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%arrayidx2.i962 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 3
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; 1 = MemoryDef(LoE)
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store i32 undef, i32* %arrayidx2.i962, align 4
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%arrayidx3.i963 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 4
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; MemoryUse(LoE)
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%3 = load %struct.gnode.0.1.3.6.9.18.20.79**, %struct.gnode.0.1.3.6.9.18.20.79*** @gnodeArray, align 8
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%arrayidx6.i968 = getelementptr inbounds %struct.gnode.0.1.3.6.9.18.20.79*, %struct.gnode.0.1.3.6.9.18.20.79** %3, i64 undef
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; MemoryUse(1) MayAlias
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%4 = load %struct.gnode.0.1.3.6.9.18.20.79*, %struct.gnode.0.1.3.6.9.18.20.79** %arrayidx6.i968, align 8
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br i1 undef, label %for.cond26.preheader.i974, label %if.then20.for.body_crit_edge.i999
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for.cond26.preheader.i974: ; preds = %if.then20.i996
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%5 = bitcast [5 x i32]* %exl.i to i8*
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%arrayidx.i924 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 1
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%arrayidx1.i925 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 2
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%arrayidx2.i926 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 3
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%arrayidx3.i927 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 4
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unreachable
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if.then20.for.body_crit_edge.i999: ; preds = %if.then20.i996
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%arrayidx9.phi.trans.insert.i997 = getelementptr inbounds [5 x i32], [5 x i32]* %exl.i, i64 0, i64 undef
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unreachable
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}
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