[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 ↗

(On Diff #140737)

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

1 ↗

(On Diff #140737)

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 ↗

(On Diff #140737)

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

211 ↗

(On Diff #141275)

Please change if .. else to ternary operator:

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

208 ↗

(On Diff #140737)

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

[mtrofin]

• Reduced testcase
• Using ternary operator.

llvm/trunk/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.
 }

llvm/trunk/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 }