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SimplifyCFG fix for volatile load/store.

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Fixes rdar:13349374.

Volatile loads and stores need to be preserved even if the language
standard says they are undefined. "volatile" in this context means "get
out of the way compiler, let my platform handle it".

Additionally, this is the only way I know of with llvm to write to the
first page (when hardware allows) without dropping to assembly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176599 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2013-03-07 01:03:35 +00:00
parent fe9dbe0066
commit 119003f2a2
2 changed files with 52 additions and 2 deletions
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6
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -3944,11 +3944,13 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
// Load from null is undefined.
if (LoadInst *LI = dyn_cast<LoadInst>(Use))
return LI->getPointerAddressSpace() == 0;
if (!LI->isVolatile())
return LI->getPointerAddressSpace() == 0;
// Store to null is undefined.
if (StoreInst *SI = dyn_cast<StoreInst>(Use))
return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
if (!SI->isVolatile())
return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
}
return false;
}

48
test/Transforms/SimplifyCFG/volatile-phioper.ll Normal file
View File

@ -0,0 +1,48 @@
; RUN: opt < %s -simplifycfg -S | FileCheck %s
;
; rdar:13349374
;
; SimplifyCFG should not eliminate blocks with volatile stores.
; Essentially, volatile needs to be backdoor that tells the optimizer
; it can no longer use language standard as an excuse. The compiler
; needs to expose the volatile access to the platform.
;
; CHECK: @test
; CHECK: entry:
; CHECK: @Trace
; CHECK: while.body:
; CHECK: store volatile
; CHECK: end:
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-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
define void @test(i8** nocapture %PeiServices) #0 {
entry:
%call = tail call i32 (...)* @Trace() #2
%tobool = icmp eq i32 %call, 0
br i1 %tobool, label %while.body, label %if.then
if.then: ; preds = %entry
%call1 = tail call i32 (...)* @Trace() #2
br label %while.body
while.body: ; preds = %entry, %if.then, %while.body
%Addr.017 = phi i8* [ %incdec.ptr, %while.body ], [ null, %if.then ], [ null, %entry ]
%x.016 = phi i8 [ %inc, %while.body ], [ 0, %if.then ], [ 0, %entry ]
%inc = add i8 %x.016, 1
%incdec.ptr = getelementptr inbounds i8* %Addr.017, i64 1
store volatile i8 %x.016, i8* %Addr.017, align 1
%0 = ptrtoint i8* %incdec.ptr to i64
%1 = trunc i64 %0 to i32
%cmp = icmp ult i32 %1, 4096
br i1 %cmp, label %while.body, label %end
end:
ret void
}
declare i32 @Trace(...) #1
attributes #0 = { nounwind ssp uwtable "fp-contract-model"="standard" "no-frame-pointer-elim" "no-frame-pointer-elim-non-leaf" "realign-stack" "relocation-model"="pic" "ssp-buffers-size"="8" }
attributes #1 = { "fp-contract-model"="standard" "no-frame-pointer-elim" "no-frame-pointer-elim-non-leaf" "realign-stack" "relocation-model"="pic" "ssp-buffers-size"="8" }
attributes #2 = { nounwind }
!0 = metadata !{i32 1039}