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ARM: fix yet another stack-folding bug 

We were trying to fold the stack adjustment into the wrong instruction in the
situation where the entire basic-block was epilogue code. Really, it can only
ever be valid to do the folding precisely where the "add sp, ..." would be
placed so there's no need for a separate iterator to track that.

Should fix PR18136.

llvm-svn: 196493
This commit is contained in:
Tim Northover 2013-12-05 11:02:02 +00:00
parent 58e44a3447
commit e4def5e228
2 changed files with 30 additions and 6 deletions
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7
llvm/lib/Target/ARM/ARMFrameLowering.cpp
View File

@ -380,15 +380,10 @@ void ARMFrameLowering::emitEpilogue(MachineFunction &MF,
if (NumBytes != 0)
emitSPUpdate(isARM, MBB, MBBI, dl, TII, NumBytes);
} else {
MachineBasicBlock::iterator FirstPop = MBBI;
// Unwind MBBI to point to first LDR / VLDRD.
const uint16_t *CSRegs = RegInfo->getCalleeSavedRegs(&MF);
if (MBBI != MBB.begin()) {
do {
if (isPopOpcode(MBBI->getOpcode()))
FirstPop = MBBI;
--MBBI;
} while (MBBI != MBB.begin() && isCSRestore(MBBI, TII, CSRegs));
if (!isCSRestore(MBBI, TII, CSRegs))
@ -435,7 +430,7 @@ void ARMFrameLowering::emitEpilogue(MachineFunction &MF,
.addReg(FramePtr));
}
} else if (NumBytes &&
!tryFoldSPUpdateIntoPushPop(STI, MF, FirstPop, NumBytes))
!tryFoldSPUpdateIntoPushPop(STI, MF, MBBI, NumBytes))
emitSPUpdate(isARM, MBB, MBBI, dl, TII, NumBytes);
// Increment past our save areas.

29
llvm/test/CodeGen/ARM/fold-stack-adjust.ll
View File

@ -124,3 +124,32 @@ define arm_aapcs_vfpcc double @check_vfp_no_return_clobber() minsize {
ret double 1.0
}
@dbl = global double 0.0
; PR18136: there was a bug determining where the first eligible pop in a
; basic-block was when the entire block was epilogue code.
define void @test_fold_point(i1 %tst) minsize {
; CHECK-LABEL: test_fold_point:
; Important to check for beginning of basic block, because if it gets
; if-converted the test is probably no longer checking what it should.
; CHECK: {{LBB[0-9]+_2}}:
; CHECK-NEXT: vpop {d7, d8}
; CHECK-NEXT: pop {r4, pc}
; We want some memory so there's a stack adjustment to fold...
%var = alloca i8, i32 8
; We want a long-lived floating register so that a callee-saved dN is used and
; there's both a vpop and a pop.
%live_val = load double* @dbl
br i1 %tst, label %true, label %end
true:
call void @bar(i8* %var)
store double %live_val, double* @dbl
br label %end
end:
; We want the epilogue to be the only thing in a basic block so that we hit
; the correct edge-case (first inst in block is correct one to adjust).
ret void
}