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[AliasAnalysis] Treat invariant.start as read-memory
Summary: We teach alias analysis that invariant.start is readonly. This helps with GVN and memcopy optimizations that currently treat. invariant.start as a clobber. We need to treat this as readonly, so that DSE does not incorrectly remove stores prior to the invariant.start Reviewers: sanjoy, reames, majnemer, dberlin Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D23214 llvm-svn: 278138
This commit is contained in:
Anna Thomas
parent
366c1adb94
commit
db9853f118
@ -781,6 +781,32 @@ ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS,
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if (isIntrinsicCall(CS, Intrinsic::experimental_guard))
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return MRI_Ref;
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// Like assumes, invariant.start intrinsics were also marked as arbitrarily
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// writing so that proper control dependencies are maintained but they never
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// mod any particular memory location visible to the IR.
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// *Unlike* assumes (which are now modeled as NoModRef), invariant.start
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// intrinsic is now modeled as reading memory. This prevents hoisting the
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// invariant.start intrinsic over stores. Consider:
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// *ptr = 40;
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// *ptr = 50;
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// invariant_start(ptr)
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// int val = *ptr;
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// print(val);
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//
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// This cannot be transformed to:
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//
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// *ptr = 40;
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// invariant_start(ptr)
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// *ptr = 50;
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// int val = *ptr;
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// print(val);
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//
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// The transformation will cause the second store to be ignored (based on
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// rules of invariant.start) and print 40, while the first program always
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// prints 50.
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if (isIntrinsicCall(CS, Intrinsic::invariant_start))
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return MRI_Ref;
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// The AAResultBase base class has some smarts, lets use them.
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return AAResultBase::getModRefInfo(CS, Loc);
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}
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34
test/Transforms/DeadStoreElimination/invariant.start.ll
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34
test/Transforms/DeadStoreElimination/invariant.start.ll
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@ -0,0 +1,34 @@
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; Test to make sure llvm.invariant.start calls are not treated as clobbers.
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; RUN: opt < %s -basicaa -dse -S | FileCheck %s
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declare {}* @llvm.invariant.start.p0i8(i64, i8* nocapture) nounwind readonly
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; We cannot remove the store 1 to %p.
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; FIXME: By the semantics of invariant.start, the store 3 to p is unreachable.
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define void @test(i8 *%p) {
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store i8 1, i8* %p, align 4
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%i = call {}* @llvm.invariant.start.p0i8(i64 1, i8* %p)
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store i8 3, i8* %p, align 4
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ret void
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; CHECK-LABEL: @test(
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; CHECK-NEXT: store i8 1, i8* %p, align 4
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; CHECK-NEXT: %i = call {}* @llvm.invariant.start.p0i8(i64 1, i8* %p)
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; CHECK-NEXT: store i8 3, i8* %p, align 4
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; CHECK-NEXT: ret void
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}
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; FIXME: We should be able to remove the first store to p, even though p and q
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; may alias.
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define void @test2(i8* %p, i8* %q) {
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store i8 1, i8* %p, align 4
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store i8 2, i8* %q, align 4
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%i = call {}* @llvm.invariant.start.p0i8(i64 1, i8* %q)
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store i8 3, i8* %p, align 4
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ret void
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; CHECK-LABEL: @test2(
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; CHECK-NEXT: store i8 1, i8* %p, align 4
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; CHECK-NEXT: store i8 2, i8* %q, align 4
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; CHECK-NEXT: %i = call {}* @llvm.invariant.start.p0i8(i64 1, i8* %q)
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; CHECK-NEXT: store i8 3, i8* %p, align 4
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; CHECK-NEXT: ret void
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}
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59
test/Transforms/GVN/invariant.start.ll
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59
test/Transforms/GVN/invariant.start.ll
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@ -0,0 +1,59 @@
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; Test to make sure llvm.invariant.start calls are not treated as clobbers.
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; RUN: opt < %s -gvn -S | FileCheck %s
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declare {}* @llvm.invariant.start.p0i8(i64, i8* nocapture) nounwind readonly
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declare void @llvm.invariant.end.p0i8({}*, i64, i8* nocapture) nounwind
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; We forward store to the load across the invariant.start intrinsic
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define i8 @forward_store() {
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; CHECK-LABEL: @forward_store
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; CHECK: call {}* @llvm.invariant.start.p0i8(i64 1, i8* %a)
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; CHECK-NOT: load
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; CHECK: ret i8 0
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%a = alloca i8
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store i8 0, i8* %a
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%i = call {}* @llvm.invariant.start.p0i8(i64 1, i8* %a)
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%r = load i8, i8* %a
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ret i8 %r
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}
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declare i8 @dummy(i8* nocapture) nounwind readonly
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; We forward store to the load in the non-local analysis case,
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; i.e. invariant.start is in another basic block.
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define i8 @forward_store_nonlocal(i1 %cond) {
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; CHECK-LABEL: forward_store_nonlocal
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; CHECK: call {}* @llvm.invariant.start.p0i8(i64 1, i8* %a)
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; CHECK: ret i8 0
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; CHECK: ret i8 %val
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%a = alloca i8
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store i8 0, i8* %a
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%i = call {}* @llvm.invariant.start.p0i8(i64 1, i8* %a)
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br i1 %cond, label %loadblock, label %exit
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loadblock:
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%r = load i8, i8* %a
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ret i8 %r
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exit:
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%val = call i8 @dummy(i8* %a)
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ret i8 %val
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}
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; We should not value forward %foo to the invariant.end corresponding to %bar.
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define i8 @forward_store1() {
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; CHECK-LABEL: forward_store1
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; CHECK: %foo = call {}* @llvm.invariant.start.p0i8
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; CHECK-NOT: load
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; CHECK: %bar = call {}* @llvm.invariant.start.p0i8
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; CHECK: call void @llvm.invariant.end.p0i8({}* %bar, i64 1, i8* %a)
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; CHECK: ret i8 0
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%a = alloca i8
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store i8 0, i8* %a
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%foo = call {}* @llvm.invariant.start.p0i8(i64 1, i8* %a)
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%r = load i8, i8* %a
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%bar = call {}* @llvm.invariant.start.p0i8(i64 1, i8* %a)
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call void @llvm.invariant.end.p0i8({}* %bar, i64 1, i8* %a)
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ret i8 %r
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}
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49
test/Transforms/MemCpyOpt/invariant.start.ll
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49
test/Transforms/MemCpyOpt/invariant.start.ll
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@ -0,0 +1,49 @@
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; MemCpy optimizations should take place even in presence of invariant.start
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; RUN: opt < %s -basicaa -memcpyopt -dse -S | FileCheck %s
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target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
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target triple = "i686-apple-darwin9"
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%0 = type { x86_fp80, x86_fp80 }
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declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture, i32, i32,
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i1) nounwind
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declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly,
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i64, i32, i1)
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declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1)
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declare {}* @llvm.invariant.start.p0i8(i64, i8* nocapture) nounwind readonly
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; FIXME: The invariant.start does not modify %P.
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; The intermediate alloca and one of the memcpy's should be eliminated, the
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; other should be transformed to a memmove.
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define void @test1(i8* %P, i8* %Q) nounwind {
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%memtmp = alloca %0, align 16
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%R = bitcast %0* %memtmp to i8*
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call void @llvm.memcpy.p0i8.p0i8.i32(i8* %R, i8* %P, i32 32, i32 16, i1 false)
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%i = call {}* @llvm.invariant.start.p0i8(i64 32, i8* %P)
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call void @llvm.memcpy.p0i8.p0i8.i32(i8* %Q, i8* %R, i32 32, i32 16, i1 false)
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ret void
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; CHECK-LABEL: @test1(
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; CHECK-NEXT: %memtmp = alloca %0, align 16
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; CHECK-NEXT: %R = bitcast %0* %memtmp to i8*
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; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %R, i8* %P, i32 32, i32 16, i1 false)
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; CHECK-NEXT: %i = call {}* @llvm.invariant.start.p0i8(i64 32, i8* %P)
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; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %Q, i8* %R, i32 32, i32 16, i1 false)
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; CHECK-NEXT: ret void
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}
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; The invariant.start intrinsic does not inhibit tranforming the memcpy to a
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; memset.
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define void @test2(i8* %dst1, i8* %dst2, i8 %c) {
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; CHECK-LABEL: define void @test2(
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; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* %dst1, i8 %c, i64 128, i32 1, i1 false)
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; CHECK-NEXT: %i = call {}* @llvm.invariant.start.p0i8(i64 32, i8* %dst1)
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; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* %dst2, i8 %c, i64 128, i32 8, i1 false)
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; CHECK-NEXT: ret void
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call void @llvm.memset.p0i8.i64(i8* %dst1, i8 %c, i64 128, i32 1, i1 false)
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%i = call {}* @llvm.invariant.start.p0i8(i64 32, i8* %dst1)
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call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst2, i8* %dst1, i64 128, i32 8, i1 false)
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ret void
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}
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