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684ae57b8e
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 $12, %rsp
ret
Fewer instructions and less register use = faster compiles.
llvm-svn: 113102
35 lines
822 B
LLVM
35 lines
822 B
LLVM
; RUN: llc < %s -fast-isel -mtriple=i386-apple-darwin | FileCheck %s
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@src = external global i32
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; rdar://6653118
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define i32 @loadgv() nounwind {
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entry:
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%0 = load i32* @src, align 4
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%1 = load i32* @src, align 4
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%2 = add i32 %0, %1
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store i32 %2, i32* @src
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ret i32 %2
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; This should fold one of the loads into the add.
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; CHECK: loadgv:
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; CHECK: movl L_src$non_lazy_ptr, %ecx
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; CHECK: movl (%ecx), %eax
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; CHECK: addl (%ecx), %eax
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; CHECK: movl %eax, (%ecx)
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; CHECK: ret
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}
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%stuff = type { i32 (...)** }
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@LotsStuff = external constant [4 x i32 (...)*]
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define void @t(%stuff* %this) nounwind {
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entry:
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store i32 (...)** getelementptr ([4 x i32 (...)*]* @LotsStuff, i32 0, i32 2), i32 (...)*** null, align 4
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ret void
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; CHECK: _t:
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; CHECK: movl $0, %eax
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; CHECK: movl L_LotsStuff$non_lazy_ptr, %ecx
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}
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