Alex Richardson
b84be9f2f1
This allows MachineCopyPropagation to eliminate copies of constant registers such as zero registers. They were previously not being eliminated as the check for MO.clobbersPhysReg(AvailSrc) would return true for constant registers such as MIPS $zero. To avoid having to manually add the zero registers to all CalleeSavedRegs instantiations in tablegen, I instead added a new isConstant bit to the Register and set this for MIPS, RISC-V, and AArch64 zero registers. RegisterInfoEmitter.cpp looks at this flag and adds all constant registers to the preserved register mask. This may also benefit other passes but so far I have only seen differences in MachineCopyPropagation. In the future it might make sense to generate `isConstantPhysReg()` from this information. Original source: https://github.com/CTSRD-CHERI/llvm-project/commit/8588d8b81458ed6d87b674893e7752e6a6915574 Reviewed By: arsenm Differential Revision: https://reviews.llvm.org/D131958
42 lines
1.8 KiB
YAML
42 lines
1.8 KiB
YAML
# Check that we can remove the redundant save of constant registers such as $zero
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# RUN: llc -mtriple=mips64-unknown-freebsd %s -start-before=machine-cp -o - | FileCheck %s --check-prefix ASM
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# RUN: llc -mtriple=mips64-unknown-freebsd %s -verify-machineinstrs -run-pass=machine-cp -o - | FileCheck %s
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--- |
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target triple = "mips64-unknown-freebsd"
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define i32 @a() nounwind {
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; ASM-LABEL: a:
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; ASM: # %bb.0:
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; ASM-NEXT: daddiu $sp, $sp, -16
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; ASM-NEXT: sd $ra, 8($sp) # 8-byte Folded Spill
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; ASM-NEXT: jalr $25
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; ASM-NEXT: move $4, $zero
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; ASM-NEXT: move $4, $zero
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; ASM-NEXT: ld $ra, 8($sp) # 8-byte Folded Reload
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; ASM-NEXT: jr $ra
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; ASM-NEXT: daddiu $sp, $sp, 16
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ret i32 0
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}
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...
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---
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name: a
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body: |
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bb.0 (%ir-block.0):
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liveins: $a0_64, $t9_64, $ra_64, $fp_64, $gp_64
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; CHECK-LABEL: name: a
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; CHECK: liveins: $a0_64, $t9_64, $ra_64, $fp_64, $gp_64
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; CHECK-NEXT: {{ $}}
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; CHECK-NEXT: ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: $a0_64 = COPY $zero_64
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; CHECK-NEXT: JALR64Pseudo $t9_64, csr_n64, implicit-def dead $ra, implicit $a0_64, implicit $gp_64, implicit-def $sp, implicit-def $v0
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; CHECK-NEXT: ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: $a0_64 = COPY $zero_64
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; CHECK-NEXT: PseudoReturn64 undef $ra_64, implicit $v0_64, implicit killed $a0_64
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ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp
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renamable $s0_64 = COPY $zero_64
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$a0_64 = COPY renamable $s0_64
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JALR64Pseudo $t9_64, csr_n64, implicit-def dead $ra, implicit $a0_64, implicit $gp_64, implicit-def $sp, implicit-def $v0
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ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp
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$a0_64 = COPY killed renamable $s0_64
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PseudoReturn64 undef $ra_64, implicit $v0_64, implicit killed $a0_64
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...
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