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ARM: correct isPredicable for MULS in ThHUMB mode

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The ARM ARM states that CPSR may not be updated by a MUL in thumb mode.  Due to
an ordering of Thumb 2 Size Reduction and If Conversion, we would end up
generating a THUMB MULS inside an IT block.

The If Conversion pass uses the TTI isPredicable method to ensure that it can
transform a Basic Block.  However, because we only check for IT handling on
Thumb2 functions, we may miss some cases.  Even then, it only validates that the
CPSR is not *live* rather than it is not accessed.  This corrects the handling
for that particular case since the same restriction does not hold on the vast
majority of the instructions.

This does prevent the IfConversion optimization from kicking in in certain
cases, but generating correct code is more valuable.  Addresses PR20555.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215328 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Saleem Abdulrasool 2014-08-10 22:20:37 +00:00
parent 4417c25b03
commit 3e5734dc38
2 changed files with 39 additions and 0 deletions
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14
lib/Target/ARM/ARMBaseInstrInfo.cpp
View File

@ -518,6 +518,13 @@ bool ARMBaseInstrInfo::DefinesPredicate(MachineInstr *MI,
return Found;
}
static bool isCPSRDefined(const MachineInstr *MI) {
for (const auto &MO : MI->operands())
if (MO.isReg() && MO.getReg() == ARM::CPSR && (MO.isDef() || !MO.isDead()))
return true;
return false;
}
/// isPredicable - Return true if the specified instruction can be predicated.
/// By default, this returns true for every instruction with a
/// PredicateOperand.
@ -525,6 +532,13 @@ bool ARMBaseInstrInfo::isPredicable(MachineInstr *MI) const {
if (!MI->isPredicable())
return false;
// The ARM Architecture Reference Manual states that the CPSR may only be
// accessed by MUL in Thumb mode if it is outside an IT block. Thus, if CPSR
// is defined (or clobbered) by this instruction, it is not predicable.
if (MI->getOpcode() == ARM::tMUL || MI->getOpcode() == ARM::t2MUL)
if (isCPSRDefined(MI))
return false;
ARMFunctionInfo *AFI =
MI->getParent()->getParent()->getInfo<ARMFunctionInfo>();

25
test/CodeGen/ARM/2014-08-04-muls-it.ll Normal file
View File

@ -0,0 +1,25 @@
; RUN: llc -mtriple thumbv7-eabi -arm-restrict-it -filetype asm -o - %s \
; RUN: | FileCheck %s
define arm_aapcscc i32 @function(i32 %i, i32 %j) {
entry:
%cmp = icmp eq i32 %i, %j
br i1 %cmp, label %if.then, label %if.end
if.then: ; preds = %entry
%mul = mul nsw i32 %i, %i
br label %if.end
if.end: ; preds = %if.then, %entry
%i.addr.0 = phi i32 [ %mul, %if.then ], [ %i, %entry ]
ret i32 %i.addr.0
}
; CHECK-LABEL: function
; CHECK: cmp r0, r1
; CHECK: bne [[LABEL:[.*]]]
; CHECK-NOT: mulseq r0, r0, r0
; CHECK: [[LABEL]]
; CHECK: muls r0, r0, r0
; CHECK: bx lr