[PeepholeOptimizer] Don't assume bitcast def always has input

Summary:
If we have a MI marked with bitcast bits, but without input operands,
PeepholeOptimizer might crash with assert.

eg:
If we apply the changes in PPCInstrVSX.td as in this patch:

[(set v4i32:$XT, (bitconvert (v16i8 immAllOnesV)))]>;

We will get assert in PeepholeOptimizer.

```
llvm-lit llvm-project/llvm/test/CodeGen/PowerPC/build-vector-tests.ll -v

llvm-project/llvm/include/llvm/CodeGen/MachineInstr.h:417: const
llvm::MachineOperand &llvm::MachineInstr::getOperand(unsigned int)
const: Assertion `i < getNumOperands() && "getOperand() out of range!"'
failed.
```

The fix is to abort if we found out of bound access.

Reviewers: qcolombet, MatzeB, hfinkel, arsenm

Reviewed By: qcolombet

Subscribers: wdng, arsenm, steven.zhang, wuzish, nemanjai, hiraditya, kbarton, MaskRay, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65542

llvm-svn: 369261

lib/CodeGen/PeepholeOptimizer.cpp

@@ -1853,6 +1853,11 @@ ValueTrackerResult ValueTracker::getNextSourceFromBitcast() {
     SrcIdx = OpIdx;
   }
 
+  // In some rare case, Def has no input, SrcIdx is out of bound,
+  // getOperand(SrcIdx) will fail below.
+  if (SrcIdx >= Def->getNumOperands())
+    return ValueTrackerResult();
+
   // Stop when any user of the bitcast is a SUBREG_TO_REG, replacing with a COPY
   // will break the assumed guarantees for the upper bits.
   for (const MachineInstr &UseMI : MRI.use_nodbg_instructions(DefOp.getReg())) {

lib/Target/PowerPC/PPCInstrVSX.td

@@ -1314,7 +1314,7 @@ let AddedComplexity = 400 in { // Prefer VSX patterns over non-VSX patterns.
       isReMaterializable = 1 in {
     def XXLEQVOnes : XX3Form_SameOp<60, 186, (outs vsrc:$XT), (ins),
                          "xxleqv $XT, $XT, $XT", IIC_VecGeneral,
-                         [(set v4i32:$XT, (v4i32 immAllOnesV))]>;
+                         [(set v4i32:$XT, (bitconvert (v16i8 immAllOnesV)))]>;
   }
 
   def XXLORC : XX3Form<60, 170,
@@ -4103,8 +4103,6 @@ let AddedComplexity = 400 in {
   }
 
   let Predicates = [HasP8Vector] in {
-    def : Pat<(v4i32 (bitconvert (v16i8 immAllOnesV))),
-              (XXLEQVOnes)>;
     def : Pat<(v1i128 (bitconvert (v16i8 immAllOnesV))),
               (v1i128 (COPY_TO_REGCLASS(XXLEQVOnes), VSRC))>;
     def : Pat<(v2i64 (bitconvert (v16i8 immAllOnesV))),

test/CodeGen/PowerPC/bitcast-peephole.mir

@@ -0,0 +1,23 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=powerpc64le-linux-gnu -run-pass=peephole-opt -verify-machineinstrs -o - %s | FileCheck %s
+
+---
+name:            bitCast
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: bitCast
+    ; CHECK: [[XXLEQVOnes:%[0-9]+]]:vsrc = XXLEQVOnes
+    ; CHECK: $v2 = COPY [[XXLEQVOnes]]
+    ; CHECK: BLR8 implicit $lr8, implicit $rm, implicit $v2
+    %0:vsrc = XXLEQVOnes
+    $v2 = COPY %0
+    BLR8 implicit $lr8, implicit $rm, implicit $v2
+
+...
+
+# This used to hit an assertion:
+#   llvm/include/llvm/CodeGen/MachineInstr.h:417: const
+#   llvm::MachineOperand &llvm::MachineInstr::getOperand(unsigned int)
+#   const: Assertion `i < getNumOperands() && "getOperand() out of range!"' failed.
+#