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Fix handling of negative offsets for AddrModeT2_i8s4 in rewriteT2FrameIndex. 

This is a follow up to r230233 to fix something that I noticed by
inspection. The AddrModeT2_i8s4 addressing mode does not support
negative offsets. I spent a good chunk of the day trying to come up with
a testcase for this but was not successful. This addressing mode is used
to spill and restore GPRPair registers in Thumb2 code and that does not
happen often. We also make very limited used of negative offsets when
lowering frame indexes. I am going ahead with the change anyway, because
I am pretty confident that it is correct. I also added a missing assertion
to check that the low bits of the scaled offset are zero.

llvm-svn: 230297
This commit is contained in:
Bob Wilson 2015-02-24 01:37:31 +00:00
parent e977e51d71
commit 8e29dec986
1 changed files with 2 additions and 5 deletions
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7
llvm/lib/Target/ARM/Thumb2InstrInfo.cpp
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@ -575,12 +575,9 @@ bool llvm::rewriteT2FrameIndex(MachineInstr &MI, unsigned FrameRegIdx,
} else if (AddrMode == ARMII::AddrModeT2_i8s4) {
Offset += MI.getOperand(FrameRegIdx + 1).getImm() * 4;
NumBits = 10; // 8 bits scaled by 4
// MCInst operand has already scaled value.
// MCInst operand expects already scaled value.
Scale = 1;
if (Offset < 0) {
isSub = true;
Offset = -Offset;
}
assert((Offset & 3) == 0 && "Can't encode this offset!");
} else {
llvm_unreachable("Unsupported addressing mode!");
}