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[X86] Fix a bug with fetch_add(INT32_MIN) 

Summary:
Fix pr21099

The pseudocode of what we were doing (spread through two functions) was:
if (operand.doesNotFitIn32Bits())
  Opc.initializeWithFoo();
if (operand < 0)
  operand = -operand;
if (operand.doesFitIn8Bits())
  Opc.initializeWithBar();
else if (operand.doesFitIn32Bits())
  Opc.initializeWithBlah();
doStuff(Opc);

So for operand == INT32_MIN, Opc was never initialized because the operand changes
from fitting in 32 bits to not fitting, causing the various bugs/error messages
noted by pr21099.

This patch adds an extra test at the beginning for this case, and an
llvm_unreachable to have better error message if the operand ends up
not fitting in 32-bits at the end.

Test Plan: new test + make check

Reviewers: jfb

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5655

llvm-svn: 219257
This commit is contained in:
Robin Morisset 2014-10-07 23:53:57 +00:00
parent 845bb3c2fd
commit 880580b88f
2 changed files with 19 additions and 0 deletions
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9
llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
View File

@ -34,6 +34,7 @@
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include <stdint.h>
using namespace llvm;
#define DEBUG_TYPE "x86-isel"
@ -1712,6 +1713,12 @@ static SDValue getAtomicLoadArithTargetConstant(SelectionDAG *CurDAG,
// Quit if not 32-bit imm.
if ((int32_t)CNVal != CNVal)
return Val;
// Quit if INT32_MIN: it would be negated as it is negative and overflow,
// producing an immediate that does not fit in the 32 bits available for
// an immediate operand to sub. However, it still fits in 32 bits for the
// add (since it is not negated) so we can return target-constant.
if (CNVal == INT32_MIN)
return CurDAG->getTargetConstant(CNVal, NVT);
// For atomic-load-add, we could do some optimizations.
if (Op == ADD) {
// Translate to INC/DEC if ADD by 1 or -1.
@ -1824,6 +1831,8 @@ SDNode *X86DAGToDAGISel::SelectAtomicLoadArith(SDNode *Node, MVT NVT) {
Opc = AtomicOpcTbl[Op][SextConstantI64];
else if (i64immSExt32(Val.getNode()))
Opc = AtomicOpcTbl[Op][ConstantI64];
else
llvm_unreachable("True 64 bits constant in SelectAtomicLoadArith");
} else
Opc = AtomicOpcTbl[Op][I64];
break;

10
llvm/test/CodeGen/X86/pr21099.ll Normal file
View File

@ -0,0 +1,10 @@
; RUN: llc < %s -O2 -march=x86-64 -verify-machineinstrs | FileCheck %s
define void @pr21099(i64* %p) {
; CHECK-LABEL: pr21099
; CHECK: lock
; CHECK-NEXT: addq $-2147483648
; This number is INT32_MIN: 0x80000000UL
%1 = atomicrmw add i64* %p, i64 -2147483648 seq_cst
ret void
}