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Verify 'optnone' can run DAG combiner when appropriate.

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Adds a test to verify the behavior that r233153 restored: 'optnone'
does not spuriously disable the DAG combiner, and in fact there are
cases where the DAG combiner must run (even at -O0 or 'optnone') in
order for codegen to succeed.

Differential Revision: http://reviews.llvm.org/D8614


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233584 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Paul Robinson 2015-03-30 19:37:44 +00:00
parent e6d6461067
commit 103d622517
1 changed files with 73 additions and 0 deletions
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test/CodeGen/X86/dag-optnone.ll Normal file
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; RUN: llc < %s -mtriple=x86_64-pc-win32 -O0 -mattr=+avx | FileCheck %s
; Background:
; If fast-isel bails out to normal selection, then the DAG combiner will run,
; even at -O0. In principle this should not happen (those are optimizations,
; and we said -O0) but as a practical matter there are some instruction
; selection patterns that depend on the legalizations and transforms that the
; DAG combiner does.
;
; The 'optnone' attribute implicitly sets -O0 and fast-isel for the function.
; The DAG combiner was disabled for 'optnone' (but not -O0) by r221168, then
; re-enabled in r233153 because of problems with instruction selection patterns
; mentioned above. (Note: because 'optnone' is supposed to match -O0, r221168
; really should have disabled the combiner for both.)
;
; If instruction selection eventually becomes smart enough to run without DAG
; combiner, then the combiner can be turned off for -O0 (not just 'optnone')
; and this test can go away. (To be replaced by a different test that verifies
; the DAG combiner does *not* run at -O0 or for 'optnone' functions.)
;
; In the meantime, this test wants to make sure the combiner stays enabled for
; 'optnone' functions, just as it is for -O0.
; The test cases @foo[WithOptnone] prove that the same DAG combine happens
; with -O0 and with 'optnone' set. To prove this, we use a Windows triple to
; cause fast-isel to bail out (because something about the calling convention
; is not handled in fast-isel). Then we have a repeated fadd that can be
; combined into an fmul. We show that this happens in both the non-optnone
; function and the optnone function.
define float @foo(float %x) #0 {
entry:
%add = fadd fast float %x, %x
%add1 = fadd fast float %add, %x
ret float %add1
}
; CHECK-LABEL: @foo
; CHECK-NOT: add
; CHECK: mul
; CHECK-NEXT: ret
define float @fooWithOptnone(float %x) #1 {
entry:
%add = fadd fast float %x, %x
%add1 = fadd fast float %add, %x
ret float %add1
}
; CHECK-LABEL: @fooWithOptnone
; CHECK-NOT: add
; CHECK: mul
; CHECK-NEXT: ret
; The test case @bar is derived from an instruction selection failure case
; that was solved by r233153. It depends on -mattr=+avx.
; Really all we're trying to prove is that it doesn't crash any more.
@id84 = common global <16 x i32> zeroinitializer, align 64
define void @bar() #1 {
entry:
%id83 = alloca <16 x i8>, align 16
%0 = load <16 x i32>, <16 x i32>* @id84, align 64
%conv = trunc <16 x i32> %0 to <16 x i8>
store <16 x i8> %conv, <16 x i8>* %id83, align 16
ret void
}
attributes #0 = { "unsafe-fp-math"="true" }
attributes #1 = { noinline optnone "unsafe-fp-math"="true" }