[PATCH] D113230: [WebAssembly] Fix fixBrTableIndex removing instruction without checking uses

[Wouter van Oortmerssen via Phabricator via llvm-commits]

aardappel created this revision.
aardappel added reviewers: dschuff, tlively, aheejin.
Herald added subscribers: wingo, ecnelises, arphaman, sunfish, hiraditya, jgravelle-google, sbc100.
aardappel requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Fixes: https://bugs.llvm.org/show_bug.cgi?id=52352


https://reviews.llvm.org/D113230

Files:
  llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp


Index: llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
===================================================================
--- llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
+++ llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
@@ -61,9 +61,17 @@
   auto ExtMI = MF.getRegInfo().getVRegDef(MI.getOperand(0).getReg());
   if (ExtMI->getOpcode() == WebAssembly::I64_EXTEND_U_I32) {
     // Unnecessarily extending a 32-bit value to 64, remove it.
-    assert(MI.getOperand(0).getReg() == ExtMI->getOperand(0).getReg());
+    auto ExtDefReg = ExtMI->getOperand(0).getReg();
+    assert(MI.getOperand(0).getReg() == ExtDefReg);
     MI.getOperand(0).setReg(ExtMI->getOperand(1).getReg());
+    // Check if the br_table was the only user of the extend.
+    for (MachineInstr &UseMI : MF.getRegInfo().use_instructions(ExtDefReg)) {
+      if (&UseMI != &MI)
+        goto user_found;
+    }
+    // No more users of extend, delete it.
     ExtMI->eraseFromParent();
+    user_found:;
   } else {
     // Incoming 64-bit value that needs to be truncated.
     Register Reg32 =


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