[llvm] 76545d7 - [AArch64] Correctly detect X reg from W reg in isCopyImpl (#137348)

[via llvm-commits]

Author: David Green
Date: 2025-04-26T11:09:13+01:00
New Revision: 76545d7ddf5a6a928398c1fbff496d868cb35ce1

URL: https://github.com/llvm/llvm-project/commit/76545d7ddf5a6a928398c1fbff496d868cb35ce1
DIFF: https://github.com/llvm/llvm-project/commit/76545d7ddf5a6a928398c1fbff496d868cb35ce1.diff

LOG: [AArch64] Correctly detect X reg from W reg in isCopyImpl (#137348)

The MachineCopyPropagation pass was incorrectly removing copy (ORRWrs)
instruction that appeared to be a nop. The instruction should not have
been marked as a copy though, the code was incorrectly assuming that
w29 - w0 + x0 == x29, but as x29 is fp it was out of order with the other
registers.

Fixes an issue reported on #129889.

Added: 
    

Modified: 
    llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
    llvm/test/CodeGen/AArch64/copyprop.mir

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
index 8e9ac82b5acd6..1a13adc300d2b 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -10053,8 +10053,7 @@ AArch64InstrInfo::isCopyInstrImpl(const MachineInstr &MI) const {
       (!MI.getOperand(0).getReg().isVirtual() ||
        MI.getOperand(0).getSubReg() == 0) &&
       (!MI.getOperand(0).getReg().isPhysical() ||
-       MI.findRegisterDefOperandIdx(MI.getOperand(0).getReg() - AArch64::W0 +
-                                        AArch64::X0,
+       MI.findRegisterDefOperandIdx(getXRegFromWReg(MI.getOperand(0).getReg()),
                                     /*TRI=*/nullptr) == -1))
     return DestSourcePair{MI.getOperand(0), MI.getOperand(2)};
 

diff  --git a/llvm/test/CodeGen/AArch64/copyprop.mir b/llvm/test/CodeGen/AArch64/copyprop.mir
index 2454509d80862..ea68c43f3eee8 100644
--- a/llvm/test/CodeGen/AArch64/copyprop.mir
+++ b/llvm/test/CodeGen/AArch64/copyprop.mir
@@ -113,3 +113,16 @@ body: |
     $w9 = ORRWrs $wzr, $wzr, 0
     STRBBui killed renamable $w9, killed renamable $x8, 36
 ...
+---
+# CHECK-LABEL: name: make_sure_w29_and_fp_isnt_removed
+# CHECK: $w29 = ORRWrs $wzr, $w29, 0, implicit $fp, implicit-def $fp
+name:            make_sure_w29_and_fp_isnt_removed
+tracksRegLiveness: true
+frameInfo:
+  maxCallFrameSize: 32
+body: |
+  bb.0:
+    liveins: $x8, $fp
+    $w29 = ORRWrs $wzr, $w29, 0, implicit $fp, implicit-def $fp
+    renamable $q0 = LDRQroX killed renamable $x8, $fp, 0, 1
+...