[PATCH] D78157: [AArch64InstrInfo] Ignore debug insts in areCFlagsAccessedBetweenInstrs

[Vedant Kumar via Phabricator via llvm-commits]

vsk created this revision.
vsk added reviewers: t.p.northover, eastig, paquette.
Herald added subscribers: danielkiss, hiraditya, kristof.beyls.
Herald added a project: LLVM.

Fix an issue where the presence of debug info could disable a peephole
optimization due to areCFlagsAccessedBetweenInstrs returning the wrong
result.

In test/CodeGen/AArch64/arm64-csel.ll, the issue was found in the
function @foo5, in which the first compare could successfully be
optimized but not the second.

Depends on D78156 <https://reviews.llvm.org/D78156>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78157

Files:
  llvm/lib/CodeGen/PeepholeOptimizer.cpp
  llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
  llvm/test/CodeGen/AArch64/arm64-csel.ll


Index: llvm/test/CodeGen/AArch64/arm64-csel.ll
===================================================================
--- llvm/test/CodeGen/AArch64/arm64-csel.ll
+++ llvm/test/CodeGen/AArch64/arm64-csel.ll
@@ -1,4 +1,4 @@
-; RUN: llc -O3 < %s | FileCheck %s
+; RUN: llc -debugify-and-strip-all-safe -O3 < %s | FileCheck %s
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-n32:64"
 target triple = "arm64-unknown-unknown"
 
Index: llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -1186,7 +1186,8 @@
   // We iterate backward starting \p To until we hit \p From.
   for (--To; To != From; --To) {
     const MachineInstr &Instr = *To;
-
+    if (Instr.isDebugInstr())
+      continue;
     if (((AccessToCheck & AK_Write) &&
          Instr.modifiesRegister(AArch64::NZCV, TRI)) ||
         ((AccessToCheck & AK_Read) && Instr.readsRegister(AArch64::NZCV, TRI)))
Index: llvm/lib/CodeGen/PeepholeOptimizer.cpp
===================================================================
--- llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -616,6 +616,7 @@
   // Attempt to optimize the comparison instruction.
   LLVM_DEBUG(dbgs() << "Attempting to optimize compare: " << MI);
   if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) {
+    LLVM_DEBUG(dbgs() << "  -> Successfully optimized compare!\n");
     ++NumCmps;
     return true;
   }


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