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llvm-mirror/test/CodeGen/X86/fast-isel-mem.ll
Chris Lattner 684ae57b8e implement rdar://6653118 - fastisel should fold loads where possible.
Since mem2reg isn't run at -O0, we get a ton of reloads from the stack,
for example, before, this code:

int foo(int x, int y, int z) {
  return x+y+z;
}

used to compile into:

_foo:                                   ## @foo
	subq	$12, %rsp
	movl	%edi, 8(%rsp)
	movl	%esi, 4(%rsp)
	movl	%edx, (%rsp)
	movl	8(%rsp), %edx
	movl	4(%rsp), %esi
	addl	%edx, %esi
	movl	(%rsp), %edx
	addl	%esi, %edx
	movl	%edx, %eax
	addq	$12, %rsp
	ret

Now we produce:

_foo:                                   ## @foo
	subq	$12, %rsp
	movl	%edi, 8(%rsp)
	movl	%esi, 4(%rsp)
	movl	%edx, (%rsp)
	movl	8(%rsp), %edx
	addl	4(%rsp), %edx    ## Folded load
	addl	(%rsp), %edx     ## Folded load
	movl	%edx, %eax
	addq	$12, %rsp
	ret

Fewer instructions and less register use = faster compiles.

llvm-svn: 113102
2010-09-05 02:18:34 +00:00

35 lines
822 B
LLVM

; RUN: llc < %s -fast-isel -mtriple=i386-apple-darwin | FileCheck %s
@src = external global i32
; rdar://6653118
define i32 @loadgv() nounwind {
entry:
%0 = load i32* @src, align 4
%1 = load i32* @src, align 4
%2 = add i32 %0, %1
store i32 %2, i32* @src
ret i32 %2
; This should fold one of the loads into the add.
; CHECK: loadgv:
; CHECK: movl L_src$non_lazy_ptr, %ecx
; CHECK: movl (%ecx), %eax
; CHECK: addl (%ecx), %eax
; CHECK: movl %eax, (%ecx)
; CHECK: ret
}
%stuff = type { i32 (...)** }
@LotsStuff = external constant [4 x i32 (...)*]
define void @t(%stuff* %this) nounwind {
entry:
store i32 (...)** getelementptr ([4 x i32 (...)*]* @LotsStuff, i32 0, i32 2), i32 (...)*** null, align 4
ret void
; CHECK: _t:
; CHECK: movl $0, %eax
; CHECK: movl L_LotsStuff$non_lazy_ptr, %ecx
}