Change IR generation for return (in the simple case) to avoid doing silly
load/store nonsense in the epilog. For example, for:
int foo(int X) {
int A[100];
return A[X];
}
we used to generate:
%arrayidx = getelementptr inbounds [100 x i32]* %A, i32 0, i64 %idxprom ; <i32*> [#uses=1]
%tmp1 = load i32* %arrayidx ; <i32> [#uses=1]
store i32 %tmp1, i32* %retval
%0 = load i32* %retval ; <i32> [#uses=1]
ret i32 %0
}
which codegen'd to this code:
_foo: ## @foo
## BB#0: ## %entry
subq $408, %rsp ## imm = 0x198
movl %edi, 400(%rsp)
movl 400(%rsp), %edi
movslq %edi, %rax
movl (%rsp,%rax,4), %edi
movl %edi, 404(%rsp)
movl 404(%rsp), %eax
addq $408, %rsp ## imm = 0x198
ret
Now we generate:
%arrayidx = getelementptr inbounds [100 x i32]* %A, i32 0, i64 %idxprom ; <i32*> [#uses=1]
%tmp1 = load i32* %arrayidx ; <i32> [#uses=1]
ret i32 %tmp1
}
and:
_foo: ## @foo
## BB#0: ## %entry
subq $408, %rsp ## imm = 0x198
movl %edi, 404(%rsp)
movl 404(%rsp), %edi
movslq %edi, %rax
movl (%rsp,%rax,4), %eax
addq $408, %rsp ## imm = 0x198
ret
This actually does matter, cutting out 2000 lines of IR from CGStmt.ll
for example.
Another interesting effect is that altivec.h functions which are dead
now get dce'd by the inliner. Hence all the changes to
builtins-ppc-altivec.c to ensure the calls aren't dead.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@106970 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index 283f361..051ef08 100644
--- a/lib/CodeGen/CGCall.cpp
+++ b/lib/CodeGen/CGCall.cpp
@@ -373,18 +373,18 @@
// FIXME: Use better alignment / avoid requiring aligned load.
Load->setAlignment(1);
return Load;
- } else {
- // Otherwise do coercion through memory. This is stupid, but
- // simple.
- llvm::Value *Tmp = CGF.CreateTempAlloca(Ty);
- llvm::Value *Casted =
- CGF.Builder.CreateBitCast(Tmp, llvm::PointerType::getUnqual(SrcTy));
- llvm::StoreInst *Store =
- CGF.Builder.CreateStore(CGF.Builder.CreateLoad(SrcPtr), Casted);
- // FIXME: Use better alignment / avoid requiring aligned store.
- Store->setAlignment(1);
- return CGF.Builder.CreateLoad(Tmp);
}
+
+ // Otherwise do coercion through memory. This is stupid, but
+ // simple.
+ llvm::Value *Tmp = CGF.CreateTempAlloca(Ty);
+ llvm::Value *Casted =
+ CGF.Builder.CreateBitCast(Tmp, llvm::PointerType::getUnqual(SrcTy));
+ llvm::StoreInst *Store =
+ CGF.Builder.CreateStore(CGF.Builder.CreateLoad(SrcPtr), Casted);
+ // FIXME: Use better alignment / avoid requiring aligned store.
+ Store->setAlignment(1);
+ return CGF.Builder.CreateLoad(Tmp);
}
/// CreateCoercedStore - Create a store to \arg DstPtr from \arg Src,
@@ -798,8 +798,7 @@
assert(AI == Fn->arg_end() && "Argument mismatch!");
}
-void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI,
- llvm::Value *ReturnValue) {
+void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI) {
// Functions with no result always return void.
if (ReturnValue == 0) {
Builder.CreateRetVoid();
@@ -824,12 +823,32 @@
break;
case ABIArgInfo::Extend:
- case ABIArgInfo::Direct:
- // The internal return value temp always will have
- // pointer-to-return-type type.
- RV = Builder.CreateLoad(ReturnValue);
+ case ABIArgInfo::Direct: {
+ // The internal return value temp always will have pointer-to-return-type
+ // type, just do a load.
+
+ // If the instruction right before the insertion point is a store to the
+ // return value, we can elide the load, zap the store, and usually zap the
+ // alloca.
+ llvm::BasicBlock *InsertBB = Builder.GetInsertBlock();
+ llvm::StoreInst *SI = 0;
+ if (InsertBB->empty() ||
+ !(SI = dyn_cast<llvm::StoreInst>(&InsertBB->back())) ||
+ SI->getPointerOperand() != ReturnValue || SI->isVolatile()) {
+ RV = Builder.CreateLoad(ReturnValue);
+ } else {
+ // Get the stored value and nuke the now-dead store.
+ RV = SI->getValueOperand();
+ SI->eraseFromParent();
+
+ // If that was the only use of the return value, nuke it as well now.
+ if (ReturnValue->use_empty() && isa<llvm::AllocaInst>(ReturnValue)) {
+ cast<llvm::AllocaInst>(ReturnValue)->eraseFromParent();
+ ReturnValue = 0;
+ }
+ }
break;
-
+ }
case ABIArgInfo::Ignore:
break;