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| author | Sanjay Patel <spatel@rotateright.com> | 2017-06-22 23:47:15 +0000 |
|---|---|---|
| committer | Sanjay Patel <spatel@rotateright.com> | 2017-06-22 23:47:15 +0000 |
| commit | 359ae44fb45205cea2a9a8f12bae9d3748f4e2ad (patch) | |
| tree | a63014479ceec85805a42805be2191103aa87f7a /llvm/test | |
| parent | 8456411e3bd4d50c807cc6b785cb49d344081dd3 (diff) | |
| download | bcm5719-llvm-359ae44fb45205cea2a9a8f12bae9d3748f4e2ad.tar.gz bcm5719-llvm-359ae44fb45205cea2a9a8f12bae9d3748f4e2ad.zip | |
[x86] add/sub (X==0) --> sbb(cmp X, 1)
This is very similar to the transform in:
https://reviews.llvm.org/rL306040
...but in this case, we use cmp X, 1 to set the carry bit as needed.
Again, we can show that all of these are logically equivalent (although
InstCombine currently canonicalizes to a form not seen here), and if
we believe IACA, then this is the smallest/fastest code. Eg, with SNB:
| Num Of | Ports pressure in cycles | |
| Uops | 0 - DV | 1 | 2 - D | 3 - D | 4 | 5 | |
---------------------------------------------------------------------
| 1 | 1.0 | | | | | | | cmp edi, 0x1
| 2 | | 1.0 | | | | 1.0 | CP | sbb eax, eax
The larger motivation is to clean up all select-of-constants combining/lowering
because we're missing some common cases.
llvm-svn: 306072
Diffstat (limited to 'llvm/test')
| -rw-r--r-- | llvm/test/CodeGen/X86/sbb.ll | 9 |
1 files changed, 3 insertions, 6 deletions
diff --git a/llvm/test/CodeGen/X86/sbb.ll b/llvm/test/CodeGen/X86/sbb.ll index 61f639a7a95..409af00d3b2 100644 --- a/llvm/test/CodeGen/X86/sbb.ll +++ b/llvm/test/CodeGen/X86/sbb.ll @@ -75,9 +75,8 @@ define i64 @i64_select_neg1_or_0(i64 %x) { define i32 @i32_select_neg1_or_0_as_math(i32 %x) { ; CHECK-LABEL: i32_select_neg1_or_0_as_math: ; CHECK: # BB#0: -; CHECK-NEXT: xorl %eax, %eax ; CHECK-NEXT: cmpl $1, %edi -; CHECK-NEXT: sbbl $0, %eax +; CHECK-NEXT: sbbl %eax, %eax ; CHECK-NEXT: retq %cmp = icmp eq i32 %x, 0 %ext = zext i1 %cmp to i32 @@ -91,8 +90,7 @@ define i16 @i16_select_neg1_or_0_commuted(i16 %x) { ; CHECK-LABEL: i16_select_neg1_or_0_commuted: ; CHECK: # BB#0: ; CHECK-NEXT: cmpw $1, %di -; CHECK-NEXT: movw $-1, %ax -; CHECK-NEXT: sbbw $-1, %ax +; CHECK-NEXT: sbbw %ax, %ax ; CHECK-NEXT: retq %cmp = icmp ne i16 %x, 0 %sel = select i1 %cmp, i16 0, i16 -1 @@ -105,8 +103,7 @@ define i8 @i8_select_neg1_or_0_commuted_as_math(i8 %x) { ; CHECK-LABEL: i8_select_neg1_or_0_commuted_as_math: ; CHECK: # BB#0: ; CHECK-NEXT: cmpb $1, %dil -; CHECK-NEXT: movb $-1, %al -; CHECK-NEXT: sbbb $-1, %al +; CHECK-NEXT: sbbb %al, %al ; CHECK-NEXT: retq %cmp = icmp ne i8 %x, 0 %ext = zext i1 %cmp to i8 |
