[GlobalOpt] Fix support for casts in ctors.

[mtrofin]

Summary

Fixing an issue where initializations of globals where constructors use
casts were silently translated to 0-initialization.

[evgeny777]

lib/Transforms/Utils/Evaluator.cpp

208

It looks like we can get into the same trouble when evaluating GEP as well. So probably move this to getInitializer() ?

test/Transforms/GlobalOpt/static-const-bitcast.ll

2

Can you make it a bit shorter? For instance clang generated metadata is not need for test case.

[mtrofin]

• Reduced testcase

[mtrofin]

lib/Transforms/Utils/Evaluator.cpp

208

That's what I thought, too, but I'm having trouble producing a testcase. Replacing the bitcast here with a GEP (and performing the necessary adjustments) "just works".

[evgeny777]

LGTM with nit.

lib/Transforms/Utils/Evaluator.cpp

208

Well it looks like the GEP case is handled in the very beginning of ComputeLoadResult, so nothing really should be done with it

211

Please change if .. else to ternary operator:

auto *I = (MM != MutatedMemory.end) ? MM->second : getInitializer(CE->getOperand(0));
if (I)
  ConstantFoldLoadThroughBitcast(I, ...);

[mtrofin]

• Reduced testcase
• Using ternary operator.

lib/Transforms/Utils/Evaluator.cpp

if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) {
     switch (CE->getOpcode()) {
     // Handle a constantexpr getelementptr.
     case Instruction::GetElementPtr:
       if (auto *I = getInitializer(CE->getOperand(0)))
         return ConstantFoldLoadThroughGEPConstantExpr(I, CE);
       break;
     // Handle a constantexpr bitcast.
     case Instruction::BitCast:
-      if (auto *I = getInitializer(CE->getOperand(0)))
+      Constant *Val = getVal(CE->getOperand(0));
+      auto MM = MutatedMemory.find(Val);
+      auto *I = (MM != MutatedMemory.end()) ? MM->second
+                                            : getInitializer(CE->getOperand(0));
+      if (I)
         return ConstantFoldLoadThroughBitcast(
             I, P->getType()->getPointerElementType(), DL);
       break;
     }
   }
 
   return nullptr;  // don't know how to evaluate.
 }
 

test/Transforms/GlobalOpt/static-const-bitcast.ll

+; RUN: opt -globalopt %s -S -o - | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.A = type { %class.Wrapper }
+%class.Wrapper = type { i32 }
+
+$Wrapper = comdat any
+
+@kA = internal global %struct.A zeroinitializer, align 4
+; CHECK: @kA = internal unnamed_addr constant %struct.A { %class.Wrapper { i32 1036831949 } }, align 4
+
[e-mail]_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } {
+i32 65535, void ()* @_GLOBAL__sub_I_const_static.cc, i8* null }]
+
+define dso_local i32 @AsBits(float* %x) #0 {
+entry:
+  %0 = bitcast float* %x to i32*
+  %1 = load i32, i32* %0, align 4
+  ret i32 %1
+}
+
+define internal void @__cxx_global_var_init() #1 section ".text.startup" {
+entry:
+  call void @Wrapper(%class.Wrapper* getelementptr inbounds (%struct.A, %struct.A* @kA, i32 0, i32 0), float 0x3FB99999A0000000)
+  %0 = call {}* @llvm.invariant.start.p0i8(i64 4, i8* bitcast (%struct.A* @kA to i8*))
+  ret void
+}
+
+define linkonce_odr dso_local void @Wrapper(%class.Wrapper* %this, float %x) unnamed_addr #0 comdat align 2 {
+entry:
+  %x.addr = alloca float, align 4
+  store float %x, float* %x.addr, align 4
+  %store_ = getelementptr inbounds %class.Wrapper, %class.Wrapper* %this, i32 0, i32 0
+  %call = call i32 @AsBits(float* %x.addr)
+  store i32 %call, i32* %store_, align 4
+  ret void
+}
+
+declare {}* @llvm.invariant.start.p0i8(i64, i8* nocapture) #2
+
+; Function Attrs: nounwind uwtable
+define dso_local void @LoadIt(%struct.A* %c) #0 {
+entry:
+  %0 = bitcast %struct.A* %c to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %0, i8* align 4 bitcast (%struct.A* @kA to i8*), i64 4, i1 false)
+  ret void
+}
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i1) #2
+
+; Function Attrs: uwtable
+define internal void @_GLOBAL__sub_I_const_static.cc() #1 section ".text.startup" {
+entry:
+  call void @__cxx_global_var_init()
+  ret void
+}
+
+attributes #0 = { nounwind uwtable "target-cpu"="x86-64" }
+attributes #1 = { uwtable "target-cpu"="x86-64" }
+attributes #2 = { argmemonly nounwind }