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[X86] Do not use cmpxchgXXb when we need the base pointer (RBX).

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cmpxchgXXb uses RBX as one of its implicit argument. I.e., when
we use that instruction we need to clobber RBX. This is generally
fine, expect when RBX is a reserved register because in that case,
the register allocator will not track its value and will not
save and restore it when interferences occur.

rdar://problem/24851412

llvm-svn: 262759
This commit is contained in:
Quentin Colombet 2016-03-04 23:29:39 +00:00
parent a167c8861d
commit 248c4c35f1
2 changed files with 38 additions and 0 deletions
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9
lib/Target/X86/X86ISelLowering.cpp
View File

@ -21162,6 +21162,15 @@ void X86TargetLowering::ReplaceNodeResults(SDNode *N,
Results);
}
case ISD::ATOMIC_CMP_SWAP_WITH_SUCCESS: {
// If the current function needs the base pointer, RBX,
// we shouldn't use cmpxchg.
// Indeed the lowering of that instruction will clobber
// that register and since RBX will be a reserved register
// the register allocator will not make sure its value will
// be properly saved and restored around this live-range.
const X86RegisterInfo *TRI = Subtarget.getRegisterInfo();
if (TRI->hasBasePointer(DAG.getMachineFunction()))
return;
EVT T = N->getValueType(0);
assert((T == MVT::i64 || T == MVT::i128) && "can only expand cmpxchg pair");
bool Regs64bit = T == MVT::i128;

29
test/CodeGen/X86/base-pointer-and-cmpxchg.ll Normal file
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@ -0,0 +1,29 @@
; RUN: llc -mattr=+cx16 -x86-use-base-pointer=true -stackrealign -stack-alignment=32 %s -o - | FileCheck --check-prefix=CHECK --check-prefix=USE_BASE %s
; RUN: llc -mattr=+cx16 -x86-use-base-pointer=false -stackrealign -stack-alignment=32 %s -o - | FileCheck --check-prefix=CHECK --check-prefix=DONT_USE_BASE %s
; This function uses dynamic allocated stack to force the use
; of a frame pointer.
; The inline asm clobbers a bunch of registers to make sure
; the frame pointer will need to be used (for spilling in that case).
;
; Then, we check that when we use rbx as the base pointer,
; we do not use cmpxchg, since using that instruction requires
; to clobbers rbx to set the arguments of the instruction and when
; rbx is used as the base pointer, RA cannot fix the code for us.
;
; CHECK-LABEL: cmp_and_swap16:
; Check that we actually use rbx.
; USE_BASE: movq %rsp, %rbx
; USE_BASE-NOT: cmpxchg
;
; DONT_USE_BASE-NOT: movq %rsp, %rbx
; DONT_USE_BASE: cmpxchg
define i1 @cmp_and_swap16(i128 %a, i128 %b, i128* %addr, i32 %n) {
%dummy = alloca i32, i32 %n
tail call void asm sideeffect "nop", "~{rax},~{rcx},~{rdx},~{rsi},~{rdi},~{rbp},~{r8},~{r9},~{r10},~{r11},~{r12},~{r13},~{r14},~{r15}"()
%cmp = cmpxchg i128* %addr, i128 %a, i128 %b seq_cst seq_cst
%res = extractvalue { i128, i1 } %cmp, 1
%idx = getelementptr i32, i32* %dummy, i32 5
store i32 %n, i32* %idx
ret i1 %res
}