From 35b21b884e5c3447a52a74d7ffaba966b07ac81f Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 27 Jun 2010 01:06:27 +0000
Subject: 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
---
 lib/CodeGen/CodeGenFunction.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'lib/CodeGen/CodeGenFunction.cpp')

diff --git a/lib/CodeGen/CodeGenFunction.cpp b/lib/CodeGen/CodeGenFunction.cpp
index 704de3531c..696c8f5165 100644
--- a/lib/CodeGen/CodeGenFunction.cpp
+++ b/lib/CodeGen/CodeGenFunction.cpp
@@ -137,7 +137,7 @@ void CodeGenFunction::FinishFunction(SourceLocation EndLoc) {
     DI->EmitRegionEnd(CurFn, Builder);
   }
 
-  EmitFunctionEpilog(*CurFnInfo, ReturnValue);
+  EmitFunctionEpilog(*CurFnInfo);
   EmitEndEHSpec(CurCodeDecl);
 
   // If someone did an indirect goto, emit the indirect goto block at the end of
-- 
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