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Avoid fusing bitcasts with dynamic allocas if the amount-to-allocate

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might overflow.  Re-typing the alloca to a larger type (e.g. double)
hoists a shift into the alloca, potentially exposing overflow in the
expression.  rdar://problem/9265821


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132926 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Stuart Hastings 2011-06-13 18:48:49 +00:00
parent afa88eaf65
commit 7ac8f8f341
2 changed files with 65 additions and 0 deletions
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5
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@ -71,6 +71,11 @@ Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
// This requires TargetData to get the alloca alignment and size information.
if (!TD) return 0;
// Insist that the amount-to-allocate not overflow.
OverflowingBinaryOperator *OBI =
dyn_cast<OverflowingBinaryOperator>(AI.getOperand(0));
if (OBI && !(OBI->hasNoSignedWrap() || OBI->hasNoUnsignedWrap())) return 0;
const PointerType *PTy = cast<PointerType>(CI.getType());
BuilderTy AllocaBuilder(*Builder);

60
test/Transforms/InstCombine/2011-06-13-nsw-alloca.ll Normal file
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@ -0,0 +1,60 @@
; RUN: opt -S -instcombine < %s | FileCheck %s
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-n8:16:32"
target triple = "i386-apple-darwin10.0.0"
define void @fu1(i32 %parm) nounwind ssp {
%1 = alloca i32, align 4
%ptr = alloca double*, align 4
store i32 %parm, i32* %1, align 4
store double* null, double** %ptr, align 4
%2 = load i32* %1, align 4
%3 = icmp ne i32 %2, 0
br i1 %3, label %4, label %10
; <label>:4 ; preds = %0
%5 = load i32* %1, align 4
%6 = mul nsw i32 %5, 8
; With "nsw", the alloca and its bitcast can be fused:
%7 = add nsw i32 %6, 2048
; CHECK: alloca double*
%8 = alloca i8, i32 %7
%9 = bitcast i8* %8 to double*
store double* %9, double** %ptr, align 4
br label %10
; <label>:10 ; preds = %4, %0
%11 = load double** %ptr, align 4
call void @bar(double* %11)
; CHECK: ret
ret void
}
declare void @bar(double*)
define void @fu2(i32 %parm) nounwind ssp {
%1 = alloca i32, align 4
%ptr = alloca double*, align 4
store i32 %parm, i32* %1, align 4
store double* null, double** %ptr, align 4
%2 = load i32* %1, align 4
%3 = icmp ne i32 %2, 0
br i1 %3, label %4, label %10
; <label>:4 ; preds = %0
%5 = load i32* %1, align 4
%6 = mul nsw i32 %5, 8
; Without "nsw", the alloca and its bitcast cannot be fused:
%7 = add i32 %6, 2048
; CHECK: alloca i8
%8 = alloca i8, i32 %7
; CHECK-NEXT: bitcast i8*
%9 = bitcast i8* %8 to double*
store double* %9, double** %ptr, align 4
br label %10
; <label>:10 ; preds = %4, %0
%11 = load double** %ptr, align 4
call void @bar(double* %11)
ret void
}