[CodeGenPrepare] Fix bad IR created by large offset GEP splitting.

[efriedma]

Summary

Creating the IR builder, then modifying the CFG, leads to an IRBuilder where the BB and insertion point are inconsistent, so new instructions have the wrong parent.

Modified an existing test because the test wasn't covering anything useful (the "invoke" was not actually an invoke by the time we hit the code in question).

It would be nice if IRBuilder could give an assertion for this, somehow... I'll think about it.

[mstorsjo]

@spatel - Can you have a look at this patch?

[dmgreen]

Looks good to me. Apologies for the delay.

[spatel]

I've never looked at that chunk of CGP before, but the code change looks strictly safer, so LGTM too.
It would be nicer if that test file had an 'opt -codegenprepare' RUN with complete IR output, so we could see exactly what's happening there to the IR, but that could be a follow-up patch.

[mstorsjo]

@efriedma Can you commit this one, or are you having second thoughts about it?

llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp

while (LargeOffsetGEP != LargeOffsetGEPs.end()) {
           // may be splitted into several parts.
           BaseGEP = GEP;
           BaseOffset = Offset;
           NewBaseGEP = nullptr;
         }
       }
 
       // Generate a new GEP to replace the current one.
-      IRBuilder<> Builder(GEP);
+      LLVMContext &Ctx = GEP->getContext();
       Type *IntPtrTy = DL->getIntPtrType(GEP->getType());
       Type *I8PtrTy =
-          Builder.getInt8PtrTy(GEP->getType()->getPointerAddressSpace());
-      Type *I8Ty = Builder.getInt8Ty();
+          Type::getInt8PtrTy(Ctx, GEP->getType()->getPointerAddressSpace());
+      Type *I8Ty = Type::getInt8Ty(Ctx);
 
       if (!NewBaseGEP) {
         // Create a new base if we don't have one yet.  Find the insertion
         // pointer for the new base first.
         BasicBlock::iterator NewBaseInsertPt;
         BasicBlock *NewBaseInsertBB;
         if (auto *BaseI = dyn_cast<Instruction>(OldBase)) {
           // If the base of the struct is an instruction, the new base will be
while (LargeOffsetGEP != LargeOffsetGEPs.end()) {
         NewBaseGEP = OldBase;
         if (NewBaseGEP->getType() != I8PtrTy)
           NewBaseGEP = NewBaseBuilder.CreatePointerCast(NewBaseGEP, I8PtrTy);
         NewBaseGEP =
             NewBaseBuilder.CreateGEP(I8Ty, NewBaseGEP, BaseIndex, "splitgep");
         NewGEPBases.insert(NewBaseGEP);
       }
 
+      IRBuilder<> Builder(GEP);
       Value *NewGEP = NewBaseGEP;
       if (Offset == BaseOffset) {
         if (GEP->getType() != I8PtrTy)
           NewGEP = Builder.CreatePointerCast(NewGEP, GEP->getType());
       } else {
         // Calculate the new offset for the new GEP.
         Value *Index = ConstantInt::get(IntPtrTy, Offset - BaseOffset);
         NewGEP = Builder.CreateGEP(I8Ty, NewBaseGEP, Index);

llvm/trunk/test/Transforms/CodeGenPrepare/AArch64/large-offset-gep.ll

; CHECK:     str      w{{[0-9]+}}, [x{{[0-9]+}}, #4]
   store i32 %phi, i32* %gep1
   br label %while_cond
 
 while_end:
   ret void
 }
 
 declare %struct_type* @foo()
+declare void @foo2()
 
 define void @test4(i32 %n) personality i32 (...)* @__FrameHandler {
 ; CHECK-LABEL: test4
 entry:
-  %struct = invoke %struct_type* @foo() to label %while_cond unwind label %cleanup
+  br label %while_cond
 
 while_cond:
   %phi = phi i32 [ 0, %entry ], [ %i, %while_body ]
+  %struct = invoke %struct_type* @foo() to label %while_cond_x unwind label %cleanup
+
+while_cond_x:
 ; CHECK:     mov     w{{[0-9]+}}, #40000
 ; CHECK-NOT: mov     w{{[0-9]+}}, #40004
   %gep0 = getelementptr %struct_type, %struct_type* %struct, i64 0, i32 1
   %gep1 = getelementptr %struct_type, %struct_type* %struct, i64 0, i32 2
+  store i32 0, i32* %gep0
   %cmp = icmp slt i32 %phi, %n
   br i1 %cmp, label %while_body, label %while_end
 
 while_body:
 ; CHECK:     str      w{{[0-9]+}}, [x{{[0-9]+}}, #4]
   %i = add i32 %phi, 1
   store i32 %i, i32* %gep0
   store i32 %phi, i32* %gep1
   br label %while_cond
 
 while_end:
   ret void
 
 cleanup:
-  landingpad { i8*, i32 } cleanup
-  unreachable
+  %x10 = landingpad { i8*, i32 }
+          cleanup
+  call void @foo2()
+  resume { i8*, i32 } %x10
 }
 
 declare i32 @__FrameHandler(...)
 
 define void @test5([65536 x i32]** %s, i32 %n) {
 ; CHECK-LABEL: test5
 entry:
   %struct = load [65536 x i32]*, [65536 x i32]** %s