[PowerPC] Check if the latch block is in the value list for the PHI before get the incoming value.

[Esme]

Summary

Fixes #60990.
There is a crash reported during Running pass 'Prepare loop for ppc preferred instruction forms'. The crash occurs in 32bit PowerPC.

[shchenz]

llvm/test/CodeGen/PowerPC/loop-instr-form-non-inc.ll

6

This is a reduced case from bugpoint:

define dso_local void @test_no_inc() local_unnamed_addr align 2 {
entry:
  %call = tail call noundef i32 @_ZN1e1fEv()
  %cmp10 = icmp sgt i32 %call, 0
  br label %for.cond

for.cond:                                         ; preds = %for.cond.cleanup, %entry
  %g.0 = phi i32 [ 1, %entry ], [ %g.1.lcssa, %for.cond.cleanup ]
  br i1 %cmp10, label %for.body.preheader, label %for.cond.cleanup

for.body.preheader:                               ; preds = %for.cond
  %0 = add i32 %call, %g.0
  br label %for.cond.cleanup

for.cond.cleanup:                                 ; preds = %for.body.preheader, %for.cond
  %g.1.lcssa = phi i32 [ %g.0, %for.cond ], [ %0, %for.body.preheader ]
  %arrayidx5 = getelementptr inbounds i8, ptr null, i32 %g.1.lcssa
  store i8 0, ptr %arrayidx5, align 1
  br label %for.cond
}

declare noundef i32 @_ZN1e1fEv() local_unnamed_addr

This should be able to further reduce, for example, using a parameter for %call, so that we can remove the external function call. And also we can add nounwind to the function, so that the cfi related instructions will not be generated.

[Esme]

Address comment.

[shchenz]

LGTM. Thank you for the fix!

Please add Fixes #60990 in the summary and the commit message.

llvm/lib/Target/PowerPC/PPCLoopInstrFormPrep.cpp

for (auto &CurrentPHI : PHIIter) {
 
     const SCEV *PHIBasePtrIncSCEV = PHIBasePtrSCEV->getStepRecurrence(*SE);
 
     if (!PHIBasePtrIncSCEV || (PHIBasePtrIncSCEV != BasePtrIncSCEV))
       continue;
 
     // Get the incoming value from the loop latch and check if the value has
     // the add form with the required increment.
+    if (CurrentPHINode->getBasicBlockIndex(LatchBB) < 0)
+      continue;
     if (Instruction *I = dyn_cast<Instruction>(
             CurrentPHINode->getIncomingValueForBlock(LatchBB))) {
       Value *StrippedBaseI = I;
       while (BitCastInst *BC = dyn_cast<BitCastInst>(StrippedBaseI))
         StrippedBaseI = BC->getOperand(0);
 
       Instruction *StrippedI = dyn_cast<Instruction>(StrippedBaseI);
       if (!StrippedI)

llvm/test/CodeGen/PowerPC/loop-instr-form-non-inc.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -verify-machineinstrs -mtriple=powerpc-unknown-linux-gnu \
+; RUN:   -mcpu=pwr9 < %s | FileCheck %s
+
+define dso_local void @test_no_inc(i32 signext %a) local_unnamed_addr nounwind align 2 {
+; CHECK-LABEL: test_no_inc:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    srawi 4, 3, 31
+; CHECK-NEXT:    cmpwi 3, 0
+; CHECK-NEXT:    li 6, 1
+; CHECK-NEXT:    li 7, 0
+; CHECK-NEXT:    andc 4, 3, 4
+; CHECK-NEXT:    addi 5, 4, 1
+; CHECK-NEXT:    .p2align 5
+; CHECK-NEXT:  .LBB0_1: # %for.cond
+; CHECK-NEXT:    #
+; CHECK-NEXT:    add 8, 3, 6
+; CHECK-NEXT:    stb 7, 0(5)
+; CHECK-NEXT:    add 5, 5, 4
+; CHECK-NEXT:    iselgt 6, 8, 6
+; CHECK-NEXT:    b .LBB0_1
+entry:
+  %cmp10 = icmp sgt i32 %a, 0
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond.cleanup, %entry
+  %g.0 = phi i32 [ 1, %entry ], [ %g.1.lcssa, %for.cond.cleanup ]
+  br i1 %cmp10, label %for.body.preheader, label %for.cond.cleanup
+
+for.body.preheader:                               ; preds = %for.cond
+  %0 = add i32 %a, %g.0
+  br label %for.cond.cleanup
+
+for.cond.cleanup:                                 ; preds = %for.body.preheader, %for.cond
+  %g.1.lcssa = phi i32 [ %g.0, %for.cond ], [ %0, %for.body.preheader ]
+  %arrayidx5 = getelementptr inbounds i8, ptr null, i32 %g.1.lcssa
+  store i8 0, ptr %arrayidx5, align 1
+  br label %for.cond
+}