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[SelectionDAG] Fix constant offset folding to avoid commuting non-commutative operators.

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This fixes a miscompile in MultiSource/Benchmarks/MiBench/consumer-lame
introduced in r258296.

llvm-svn: 258366
This commit is contained in:
Dan Gohman 2016-01-20 23:16:59 +00:00
parent 0c74edaf2c
commit 2536ce124f
2 changed files with 21 additions and 2 deletions
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1
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -3312,6 +3312,7 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, SDLoc DL, EVT VT,
// fold (add Sym, c) -> Sym+c
if (GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Cst1))
return FoldSymbolOffset(Opcode, VT, GA, Cst2);
if (isCommutativeBinOp(Opcode))
if (GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Cst2))
return FoldSymbolOffset(Opcode, VT, GA, Cst1);

18
test/CodeGen/X86/negative-offset.ll Normal file
View File

@ -0,0 +1,18 @@
; RUN: llc < %s -asm-verbose=false | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
; Test that a constant consisting of a global symbol with a negative offset
; is properly folded and isel'd.
; CHECK-LABEL: negative_offset:
; CHECK: movl $G, %eax
; CHECK: notq %rax
; CHECK: addq %rdi, %rax
; CHECK: retq
@G = external global [8 x i32]
define i8* @negative_offset(i8* %a) {
%t = getelementptr i8, i8* %a, i64 sub (i64 -1, i64 ptrtoint ([8 x i32]* @G to i64))
ret i8* %t
}