[WebAssembly] Fix memory bug introduced in 52861809994c

Summary:
The instruction at `DefI` can sometimes be destroyed by
`rematerializeCheapDef`, so it should not be used after calling that
function. The fix is to use `Insert` instead when examining additional
multivalue stackifications. `Insert` is the address of the new
defining instruction after all moves and rematerializations have taken
place.

Reviewers: aheejin

Subscribers: dschuff, sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74875

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
index ad4a95c..82f752f 100644 (file)
--- a/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
@@ -923,9 +923,9 @@ bool WebAssemblyRegStackify::runOnMachineFunction(MachineFunction &MF) {
         // Stackifying a multivalue def may unlock in-place stackification of
         // subsequent defs. TODO: Handle the case where the consecutive uses are
         // not all in the same instruction.
-        auto *SubsequentDef = DefI->defs().begin();
+        auto *SubsequentDef = Insert->defs().begin();
         auto *SubsequentUse = &Use;
-        while (SubsequentDef != DefI->defs().end() &&
+        while (SubsequentDef != Insert->defs().end() &&
                SubsequentUse != Use.getParent()->uses().end()) {
           if (!SubsequentDef->isReg() || !SubsequentUse->isReg())
             break;