[GlobalOpt] Don't remove inalloca from musttail-called functions

[hans]

Summary

Otherwise the verifier complains about the mismatching function ABIs.

[hans]

Please take a look!

(We're hitting this in the Chromium browser / compiler test suite, https://crbug.com/1101286)

[aeubanks]

LGTM
Ideally we could look remove musttail inalloca calls/parameters recursively

llvm/lib/Transforms/IPO/GlobalOpt.cpp

if (!F->hasLocalLinkage())
       continue;
 
     // If we have an inalloca parameter that we can safely remove the
     // inalloca attribute from, do so. This unlocks optimizations that
     // wouldn't be safe in the presence of inalloca.
     // FIXME: We should also hoist alloca affected by this to the entry
     // block if possible.
     if (F->getAttributes().hasAttrSomewhere(Attribute::InAlloca) &&
-        !F->hasAddressTaken()) {
+        !F->hasAddressTaken() && !hasMustTailCallers(F)) {
       RemoveAttribute(F, Attribute::InAlloca);
       Changed = true;
     }
 
     // FIXME: handle invokes
     // FIXME: handle musttail
     if (F->getAttributes().hasAttrSomewhere(Attribute::Preallocated)) {
       if (!F->hasAddressTaken() && !hasMustTailCallers(F) &&

llvm/test/Transforms/GlobalOpt/fastcc.ll

 }
 
 define internal i32 @inalloca(i32* inalloca %p) {
 ; CHECK-LABEL: define internal fastcc i32 @inalloca(i32* %p)
   %rv = load i32, i32* %p
   ret i32 %rv
 }
 
+define i32 @inalloca2_caller(i32* inalloca %p) {
+  %rv = musttail call i32 @inalloca2(i32* inalloca %p)
+  ret i32 %rv
+}
+define internal i32 @inalloca2(i32* inalloca %p) {
+; Because of the musttail caller, this inalloca cannot be dropped.
+; CHECK-LABEL: define internal i32 @inalloca2(i32* inalloca %p)
+  %rv = load i32, i32* %p
+  ret i32 %rv
+}
+
 define internal i32 @preallocated(i32* preallocated(i32) %p) {
 ; CHECK-LABEL: define internal fastcc i32 @preallocated(i32* %p)
   %rv = load i32, i32* %p
   ret i32 %rv
 }
 
 define void @call_things() {
   %m = alloca i32