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| author | Benjamin Kramer <benny.kra@googlemail.com> | 2010-07-08 11:39:10 +0000 |
|---|---|---|
| committer | Benjamin Kramer <benny.kra@googlemail.com> | 2010-07-08 11:39:10 +0000 |
| commit | 1db071f0dae25d0c5a1af61ca71fa20d0a8e9370 (patch) | |
| tree | 932a47f727c526ffbe4b42d99a819b9b3b669e83 /lib/Target/README.txt | |
| parent | 67f8a7bc26c2993854a7e9ab43af362bc4477e3f (diff) | |
| download | llvm-1db071f0dae25d0c5a1af61ca71fa20d0a8e9370.tar.gz llvm-1db071f0dae25d0c5a1af61ca71fa20d0a8e9370.tar.bz2 llvm-1db071f0dae25d0c5a1af61ca71fa20d0a8e9370.tar.xz | |
Teach instcombine to transform
(X >s -1) ? C1 : C2 and (X <s 0) ? C2 : C1
into ((X >>s 31) & (C2 - C1)) + C1, avoiding the conditional.
This optimization could be extended to take non-const C1 and C2 but we better
stay conservative to avoid code size bloat for now.
for
int sel(int n) {
return n >= 0 ? 60 : 100;
}
we now generate
sarl $31, %edi
andl $40, %edi
leal 60(%rdi), %eax
instead of
testl %edi, %edi
movl $60, %ecx
movl $100, %eax
cmovnsl %ecx, %eax
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107866 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/README.txt')
| -rw-r--r-- | lib/Target/README.txt | 11 |
1 files changed, 0 insertions, 11 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 90afe3640c..4d7ee08de1 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -906,17 +906,6 @@ The expression should optimize to something like //===---------------------------------------------------------------------===// -From GCC Bug 3756: -int -pn (int n) -{ - return (n >= 0 ? 1 : -1); -} -Should combine to (n >> 31) | 1. Currently not optimized with "clang --emit-llvm-bc | opt -std-compile-opts | llc". - -//===---------------------------------------------------------------------===// - void a(int variable) { if (variable == 4 || variable == 6) |