[PowerPC] Avoid working on deleted node in ext bool trunc combine (#160050)

This code was already creating HandleSDNodes to handle the case where a
node gets replaced with an equivalent node. However, the code before the
handles are created also performs RAUW operations, which can end up
CSEing and deleting nodes.

Fix this issue by moving the handle creation earlier.

Fixes #160040.

Author: nikic

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -15411,6 +15411,12 @@ SDValue PPCTargetLowering::DAGCombineExtBoolTrunc(SDNode *N,
     }
   }
 
+  // Convert PromOps to handles before doing any RAUW operations, as these
+  // may CSE with existing nodes, deleting the originals.
+  std::list<HandleSDNode> PromOpHandles;
+  for (auto &PromOp : PromOps)
+    PromOpHandles.emplace_back(PromOp);
+
   // Replace all inputs, either with the truncation operand, or a
   // truncation or extension to the final output type.
   for (unsigned i = 0, ie = Inputs.size(); i != ie; ++i) {
@@ -15434,10 +15440,6 @@ SDValue PPCTargetLowering::DAGCombineExtBoolTrunc(SDNode *N,
         DAG.getAnyExtOrTrunc(InSrc, dl, N->getValueType(0)));
   }
 
-  std::list<HandleSDNode> PromOpHandles;
-  for (auto &PromOp : PromOps)
-    PromOpHandles.emplace_back(PromOp);
-
   // Replace all operations (these are all the same, but have a different
   // (promoted) return type). DAG.getNode will validate that the types of
   // a binary operator match, so go through the list in reverse so that

llvm/test/CodeGen/PowerPC/pr160040.ll

@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
+
+; Make sure this does not crash.
+define i32 @test(i32 %arg) {
+; CHECK-LABEL: test:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    rlwinm 4, 3, 13, 19, 19
+; CHECK-NEXT:    rlwinm 3, 3, 2, 30, 30
+; CHECK-NEXT:    xori 4, 4, 4096
+; CHECK-NEXT:    xori 3, 3, 2
+; CHECK-NEXT:    rlwimi 3, 4, 0, 31, 29
+; CHECK-NEXT:    blr
+  %icmp = icmp sgt i32 %arg, -1
+  %select = select i1 %icmp, i16 1, i16 0
+  %select1 = select i1 %icmp, i16 16384, i16 0
+  %lshr = lshr i16 %select1, 1
+  %zext = zext i16 %lshr to i32
+  %lshr2 = lshr i32 %zext, 1
+  %shl = shl i16 %select, 1
+  %zext3 = zext i16 %shl to i32
+  %or = or i32 %lshr2, %zext3
+  ret i32 %or
+}