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[LICM] Hoist calls to readonly argmemonly functions even with stores in the loop

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We know that an argmemonly function can only access memory pointed to by it's pointer arguments. Rather than needing to consider all possible stores as aliasing (as we do for a readonly function), we can only consider the aliasing of the pointer arguments.

Note that this change only addresses hoisting. I'm thinking about how to address speculation safety as well, but that will be a different change.

FYI, argmemonly disallows accessing memory through non-pointer typed arguments.  

Differential Revision: http://reviews.llvm.org/D12771




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248220 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Philip Reames 2015-09-21 22:27:59 +00:00
parent 270b82ade0
commit 8ea1f82142
2 changed files with 80 additions and 0 deletions
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11
lib/Transforms/Scalar/LICM.cpp
View File

@ -471,6 +471,17 @@ bool canSinkOrHoistInst(Instruction &I, AliasAnalysis *AA, DominatorTree *DT,
if (Behavior == FMRB_DoesNotAccessMemory)
return true;
if (AliasAnalysis::onlyReadsMemory(Behavior)) {
// A readonly argmemonly function only reads from memory pointed to by
// it's arguments with arbitrary offsets. If we can prove there are no
// writes to this memory in the loop, we can hoist or sink.
if (AliasAnalysis::onlyAccessesArgPointees(Behavior)) {
for (Value *Op : CI->arg_operands())
if (Op->getType()->isPointerTy() &&
pointerInvalidatedByLoop(Op, MemoryLocation::UnknownSize,
AAMDNodes(), CurAST))
return false;
return true;
}
// If this call only reads from memory and there are no writes to memory
// in the loop, we can hoist or sink the call as appropriate.
bool FoundMod = false;

69
test/Transforms/LICM/argmemonly-call.ll Normal file
View File

@ -0,0 +1,69 @@
; RUN: opt -S -basicaa -licm %s | FileCheck %s
declare i32 @foo() readonly argmemonly nounwind
declare i32 @foo2() readonly nounwind
declare i32 @bar(i32* %loc2) readonly argmemonly nounwind
define void @test(i32* %loc) {
; CHECK-LABEL: @test
; CHECK: @foo
; CHECK-LABEL: loop:
br label %loop
loop:
%res = call i32 @foo()
store i32 %res, i32* %loc
br label %loop
}
; Negative test: show argmemonly is required
define void @test_neg(i32* %loc) {
; CHECK-LABEL: @test_neg
; CHECK-LABEL: loop:
; CHECK: @foo
br label %loop
loop:
%res = call i32 @foo2()
store i32 %res, i32* %loc
br label %loop
}
define void @test2(i32* noalias %loc, i32* noalias %loc2) {
; CHECK-LABEL: @test2
; CHECK: @bar
; CHECK-LABEL: loop:
br label %loop
loop:
%res = call i32 @bar(i32* %loc2)
store i32 %res, i32* %loc
br label %loop
}
; Negative test: %might clobber gep
define void @test3(i32* %loc) {
; CHECK-LABEL: @test3
; CHECK-LABEL: loop:
; CHECK: @bar
br label %loop
loop:
%res = call i32 @bar(i32* %loc)
%gep = getelementptr i32, i32 *%loc, i64 1000000
store i32 %res, i32* %gep
br label %loop
}
; Negative test: %loc might alias %loc2
define void @test4(i32* %loc, i32* %loc2) {
; CHECK-LABEL: @test4
; CHECK-LABEL: loop:
; CHECK: @bar
br label %loop
loop:
%res = call i32 @bar(i32* %loc2)
store i32 %res, i32* %loc
br label %loop
}