[GlobalOpt] Fix the load types when OptimizeGlobalAddressOfMalloc

[scui]

Summary

Currently, in OptimizeGlobalAddressOfMalloc, the transformation for global loads assumes that they have the same Type. With the support of ConstantExpr (https://reviews.llvm.org/D106589), this may not be true any more (as seen in the test case), and we miss the code to handle this, This is to fix that.

Hopefully, this is the problem that @saugustine reported in https://reviews.llvm.org/D106589. The test case I added here has the similar msg you have. Please verify. Thanks.

[efriedma]

llvm/lib/Transforms/IPO/GlobalOpt.cpp

1000

Why do you need to mess with the way you're iterating over the uses of LI? Calling ConstantExpr::getBitCast() doesn't mess with the use-list of LI.

1004

Is RepValue dead with this change?

[saugustine]

I need to test a little more extensively, but this does appear to fix the issue I had reported, which is good news. Thanks.

[scui]

llvm/lib/Transforms/IPO/GlobalOpt.cpp

1000

I guess I have a preference on for loop. I'll change it back.

1004

Will add code to make use of it like the original code.

[scui]

To address review comments

[efriedma]

LGTM

llvm/lib/Transforms/IPO/GlobalOpt.cpp

if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
                         !isa<ConstantPointerNull>(SI->getValueOperand())),
                     InitBool, false, Align(1), SI->getOrdering(),
                     SI->getSyncScopeID(), SI);
       SI->eraseFromParent();
       continue;
     }
 
     LoadInst *LI = cast<LoadInst>(U);
-    while (!LI->use_empty()) {
-      Use &LoadUse = *LI->use_begin();
-      ICmpInst *ICI = dyn_cast<ICmpInst>(LoadUse.getUser());
+    for (Use &LU : llvm::make_early_inc_range(LI->uses())) {
+      ICmpInst *ICI = dyn_cast<ICmpInst>(LU.getUser());
       if (!ICI) {
-        LoadUse = RepValue;
+        // Simply replace the use by the NewGV.
+        LU.set(ConstantExpr::getBitCast(NewGV, LI->getType()));
         continue;
       }
 
       // Replace the cmp X, 0 with a use of the bool value.
       Value *LV = new LoadInst(InitBool->getValueType(), InitBool,
                                InitBool->getName() + ".val", false, Align(1),
                                LI->getOrdering(), LI->getSyncScopeID(), LI);
       InitBoolUsed = true;

llvm/test/Transforms/GlobalOpt/2021-08-03-StoreOnceLoadMultiCasts.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -globalopt -S < %s | FileCheck %s
+; RUN: opt -passes=globalopt -S < %s | FileCheck %s
+
+@g = internal global i32* null, align 8
+
+define signext i32 @f() local_unnamed_addr {
+; CHECK-LABEL: @f(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    store i32 1, i32* @g.body, align 4
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    store i8 2, i8* bitcast (i32* @g.body to i8*), align 4
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  %call = call i8* @malloc(i64 4)
+  %b = bitcast i8* %call to i32*
+  store i32* %b, i32** @g, align 8
+  call void @f1()
+  %0 = load i32*, i32** @g, align 8
+  store i32 1, i32* %0, align 4
+  call void @f1()
+  %1 = load i8*, i8** bitcast (i32** @g to i8**), align 8
+  store i8 2, i8* %1, align 4
+  ret i32 1
+}
+
+define signext i32 @main() {
+; CHECK-LABEL: @main(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CALL:%.*]] = call signext i32 @f()
+; CHECK-NEXT:    [[TMP0:%.*]] = load i32, i32* @g.body, align 4
+; CHECK-NEXT:    ret i32 [[TMP0]]
+;
+entry:
+  %call = call signext i32 @f()
+  %0 = load i32*, i32** @g, align 8
+  %1 = load i32, i32* %0, align 4
+  ret i32 %1
+}
+
+declare noalias align 16 i8* @malloc(i64)
+declare void @f1()