[PATCH] D65315: [PowerPC][Peephole] Check if `extsw`'s second operand is a virtual register

[Kai Luo via Phabricator via llvm-commits]

lkail created this revision.
lkail added reviewers: hfinkel, steven.zhang, jsji, nemanjai, shchenz.
Herald added subscribers: llvm-commits, MaskRay, kbarton, hiraditya.
Herald added a project: LLVM.

When combining `extsw` and `sldi` in `PPCMIPeephole`, we have to check if `extsw`'s second operand is a virtual register, otherwise we might get miscompile. For now, I haven't find a real world case, so I posted a MIR test case.


Repository:
  rL LLVM

https://reviews.llvm.org/D65315

Files:
  llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
  llvm/test/CodeGen/MIR/PowerPC/peephole-miscompile-extswsli.mir


Index: llvm/test/CodeGen/MIR/PowerPC/peephole-miscompile-extswsli.mir
===================================================================
--- llvm/test/CodeGen/MIR/PowerPC/peephole-miscompile-extswsli.mir
+++ llvm/test/CodeGen/MIR/PowerPC/peephole-miscompile-extswsli.mir
@@ -20,10 +20,11 @@
   ; CHECK:   B %bb.1
   ; CHECK: bb.1:
   ; CHECK:   liveins: $x3
+  ; CHECK:   [[EXTSW:%[0-9]+]]:g8rc = EXTSW $x3
   ; CHECK:   [[RLDICR:%[0-9]+]]:g8rc = RLDICR [[ANDIo8_]], 2, 61
   ; CHECK:   $x3 = COPY [[RLDICR]]
-  ; CHECK:   [[EXTSWSLI:%[0-9]+]]:g8rc = EXTSWSLI $x3, 2, implicit-def $carry
-  ; CHECK:   [[ADD8_:%[0-9]+]]:g8rc = ADD8 [[COPY3]], [[EXTSWSLI]]
+  ; CHECK:   [[RLDICR1:%[0-9]+]]:g8rc = RLDICR [[EXTSW]], 2, 61
+  ; CHECK:   [[ADD8_:%[0-9]+]]:g8rc = ADD8 [[COPY3]], [[RLDICR1]]
   ; CHECK:   $x3 = COPY [[ADD8_]]
   ; CHECK:   BLR8 implicit $lr8, implicit $rm, implicit $x3
   ; CHECK: bb.2:
Index: llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
+++ llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
@@ -1428,6 +1428,12 @@
   if (!MRI->hasOneNonDBGUse(SrcReg))
     return false;
 
+  assert(SrcMI->getNumOperands() == 2 && "EXTSW should have 2 operands");
+  assert(SrcMI->getOperand(1).isReg() &&
+         "EXTSW's second operand should be a register");
+  if (!TargetRegisterInfo::isVirtualRegister(SrcMI->getOperand(1).getReg()))
+    return false;
+
   LLVM_DEBUG(dbgs() << "Combining pair: ");
   LLVM_DEBUG(SrcMI->dump());
   LLVM_DEBUG(MI.dump());


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