[llvm-bugs] [Bug 46386] New: Miscompile with inalloca/exception/inlining

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46386

            Bug ID: 46386
           Summary: Miscompile with inalloca/exception/inlining
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: aeubanks at google.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

Brought up in https://reviews.llvm.org/D80951.

```
#include <cstdio>

struct A {
  __attribute((optnone)) A(int) noexcept { z[1] = 10; }
  __attribute((optnone)) A() {
    z[1] = 5;
    throw 1;
  }
  __attribute((optnone)) ~A() { printf("%d %p\n", z[1], this); }
  int z[10000];
};

__attribute((optnone)) void foo(int z, A a) noexcept {}

__attribute((always_inline)) static int inner() {
  try {
    foo(1, A());
  } catch (...) {
  }
  return 3;
}

void bar() {
  for (int i = 0; i < 10; ++i) {
    foo(inner(), A(1));
  }
}

int main() { bar(); }
```

seems to be miscompiled on Win32. It should print "10 XXXXXXXX" where XXXXXXXX
is constant (no stack leak).
But instead of "10" it prints a random (but consistent within a run) value.

LLVM IR:
```
; Function Attrs: noinline optnone
define dso_local void @"?bar@@YAXXZ"() #1 personality i8* bitcast (i32 (...)*
@__CxxFrameHandler3 to i8*) {
entry:
  %i = alloca i32, align 4
  store i32 0, i32* %i, align 4
  br label %for.cond

for.cond:                                         ; preds = %for.inc, %entry
  %0 = load i32, i32* %i, align 4
  %cmp = icmp slt i32 %0, 10
  br i1 %cmp, label %for.body, label %for.end

for.body:                                         ; preds = %for.cond
  %inalloca.save = call i8* @llvm.stacksave()
  %argmem = alloca inalloca <{ i32, %struct.A }>, align 4
  %1 = getelementptr inbounds <{ i32, %struct.A }>, <{ i32, %struct.A }>*
%argmem, i32 0, i32 1
  %call = call x86_thiscallcc %struct.A* @"??0A@@QAE at H@Z"(%struct.A* %1, i32 1)
#2
  %inalloca.save.i = call i8* @llvm.stacksave()
  %argmem.i = alloca inalloca <{ i32, %struct.A }>, align 4
  %2 = getelementptr inbounds <{ i32, %struct.A }>, <{ i32, %struct.A }>*
%argmem.i, i32 0, i32 1
  %call.i = invoke x86_thiscallcc %struct.A* @"??0A@@QAE at XZ"(%struct.A* %2)
          to label %invoke.cont.i unwind label %catch.dispatch.i

catch.dispatch.i:                                 ; preds = %for.body
  %3 = catchswitch within none [label %catch.i] unwind label %ehcleanup

catch.i:                                          ; preds = %catch.dispatch.i
  %4 = catchpad within %3 [i8* null, i32 64, i8* null]
  catchret from %4 to label %catchret.dest.i

catchret.dest.i:                                  ; preds = %catch.i
  br label %"?inner@@YAHXZ.exit"

invoke.cont.i:                                    ; preds = %for.body
  %5 = getelementptr inbounds <{ i32, %struct.A }>, <{ i32, %struct.A }>*
%argmem.i, i32 0, i32 0
  store i32 1, i32* %5, align 4
  call void @"?foo@@YAXHUA@@@Z"(<{ i32, %struct.A }>* inalloca %argmem.i) #2
  call void @llvm.stackrestore(i8* %inalloca.save.i)
  br label %"?inner@@YAHXZ.exit"

"?inner@@YAHXZ.exit":                             ; preds = %catchret.dest.i,
%invoke.cont.i
  br label %invoke.cont

invoke.cont:                                      ; preds =
%"?inner@@YAHXZ.exit"
  %6 = getelementptr inbounds <{ i32, %struct.A }>, <{ i32, %struct.A }>*
%argmem, i32 0, i32 0
  store i32 3, i32* %6, align 4
  call void @"?foo@@YAXHUA@@@Z"(<{ i32, %struct.A }>* inalloca %argmem) #2
  call void @llvm.stackrestore(i8* %inalloca.save)
  br label %for.inc

for.inc:                                          ; preds = %invoke.cont
  %7 = load i32, i32* %i, align 4
  %inc = add nsw i32 %7, 1
  store i32 %inc, i32* %i, align 4
  br label %for.cond

ehcleanup:                                        ; preds = %catch.dispatch.i
  %8 = cleanuppad within none []
  call x86_thiscallcc void @"??1A@@QAE at XZ"(%struct.A* %1) #2 [ "funclet"(token
%8) ]
  cleanupret from %8 unwind to caller

for.end:                                          ; preds = %for.cond
  ret void
}
```

Moving the `@llvm.stackrestore` in `invoke.cont.i` to instead be in
`catchret.dest.i` seems to fix this issue.

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