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b8f5ff7071
We also want to optimise tests like this: return a*b == 0. The MULS instruction is flag setting, so we don't need the CMP instruction but can instead branch on the result of the MULS. The generated instructions sequence for this example was: MULS, MOVS, MOVS, CMP. The MOVS instruction load the boolean values resulting from the select instruction, but these MOVS instructions are flag setting and were thus preventing this optimisation. Now we first reorder and move the MULS to before the CMP and generate sequence MOVS, MOVS, MULS, CMP so that the optimisation could trigger. Reordering of the MULS and MOVS is safe to do because the subsequent MOVS instructions just set the CPSR register and don't use it, i.e. the CPSR is dead. Differential Revision: https://reviews.llvm.org/D27990 llvm-svn: 292608
109 lines
2.9 KiB
YAML
109 lines
2.9 KiB
YAML
# RUN: llc -run-pass=peephole-opt %s -o - | FileCheck %s
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# Here we check that the peephole cmp rewrite is not triggered, because
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# there is store instruction between the tMUL and tCMP, i.e. there are
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# no constants to reorder.
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--- |
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; ModuleID = 'cmp2-peephole-thumb.ll'
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source_filename = "<stdin>"
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target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
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target triple = "thumb-none--eabi"
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define i32 @g(i32 %a, i32 %b) {
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entry:
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%retval = alloca i32, align 4
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%mul = alloca i32, align 4
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%mul1 = mul nsw i32 %a, %b
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store i32 %mul1, i32* %mul, align 4
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%0 = load i32, i32* %mul, align 4
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%cmp = icmp sle i32 %0, 0
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br i1 %cmp, label %if.then, label %if.end
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if.then: ; preds = %entry
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store i32 42, i32* %retval, align 4
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br label %return
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if.end: ; preds = %entry
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store i32 1, i32* %retval, align 4
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br label %return
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return: ; preds = %if.end, %if.then
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%1 = load i32, i32* %retval, align 4
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ret i32 %1
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}
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...
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---
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name: g
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# CHECK-LABEL: name: g
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alignment: 1
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exposesReturnsTwice: false
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legalized: false
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regBankSelected: false
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selected: false
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tracksRegLiveness: true
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registers:
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- { id: 0, class: tgpr }
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- { id: 1, class: tgpr }
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- { id: 2, class: tgpr }
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- { id: 3, class: tgpr }
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- { id: 4, class: tgpr }
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- { id: 5, class: tgpr }
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liveins:
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- { reg: '%r0', virtual-reg: '%0' }
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- { reg: '%r1', virtual-reg: '%1' }
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frameInfo:
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isFrameAddressTaken: false
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isReturnAddressTaken: false
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hasStackMap: false
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hasPatchPoint: false
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stackSize: 0
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offsetAdjustment: 0
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maxAlignment: 4
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adjustsStack: false
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hasCalls: false
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maxCallFrameSize: 0
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hasOpaqueSPAdjustment: false
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hasVAStart: false
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hasMustTailInVarArgFunc: false
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stack:
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- { id: 0, name: retval, offset: 0, size: 4, alignment: 4, local-offset: -4 }
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- { id: 1, name: mul, offset: 0, size: 4, alignment: 4, local-offset: -8 }
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# CHECK: tMUL
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# CHECK-NEXT: tSTRspi
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# CHECK-NEXT: tCMPi8
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body: |
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bb.0.entry:
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successors: %bb.1.if.then(0x40000000), %bb.2.if.end(0x40000000)
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liveins: %r0, %r1
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%1 = COPY %r1
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%0 = COPY %r0
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%2, %cpsr = tMUL %0, %1, 14, _
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tSTRspi %2, %stack.1.mul, 0, 14, _ :: (store 4 into %ir.mul)
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tCMPi8 %2, 0, 14, _, implicit-def %cpsr
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tBcc %bb.2.if.end, 12, %cpsr
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tB %bb.1.if.then, 14, _
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bb.1.if.then:
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successors: %bb.3.return(0x80000000)
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%4, %cpsr = tMOVi8 42, 14, _
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tSTRspi killed %4, %stack.0.retval, 0, 14, _ :: (store 4 into %ir.retval)
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tB %bb.3.return, 14, _
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bb.2.if.end:
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successors: %bb.3.return(0x80000000)
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%3, %cpsr = tMOVi8 1, 14, _
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tSTRspi killed %3, %stack.0.retval, 0, 14, _ :: (store 4 into %ir.retval)
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bb.3.return:
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%5 = tLDRspi %stack.0.retval, 0, 14, _ :: (dereferenceable load 4 from %ir.retval)
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%r0 = COPY %5
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tBX_RET 14, _, implicit %r0
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...
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