diff options
| author | Jakob Stoklund Olesen <stoklund@2pi.dk> | 2012-03-29 17:22:39 +0000 |
|---|---|---|
| committer | Jakob Stoklund Olesen <stoklund@2pi.dk> | 2012-03-29 17:22:39 +0000 |
| commit | 41e2073f623a08504e2e1e5a9fc5c9f22a03eb83 (patch) | |
| tree | c4f05adc3565dc1ccd4bdfd913e4a9b091e23fdb /lib/Transforms | |
| parent | 73478404af7f6b6e64bdda5920ebaede6a4e7a14 (diff) | |
Don't PRE compares.
CodeGenPrepare sinks compare instructions down to their uses to prevent
live flags and predicate registers across basic blocks.
PRE of a compare instruction prevents that, forcing the i1 compare
result into a general purpose register. That is usually more expensive
than the redundant compare PRE was trying to eliminate in the first
place.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153657 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Transforms')
| -rw-r--r-- | lib/Transforms/Scalar/GVN.cpp | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp index 8b79d27b95..38afe1b83d 100644 --- a/lib/Transforms/Scalar/GVN.cpp +++ b/lib/Transforms/Scalar/GVN.cpp @@ -2328,7 +2328,14 @@ bool GVN::performPRE(Function &F) { CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || isa<DbgInfoIntrinsic>(CurInst)) continue; - + + // Don't do PRE on compares. The PHI would prevent CodeGenPrepare from + // sinking the compare again, and it would force the code generator to + // move the i1 from processor flags or predicate registers into a general + // purpose register. + if (isa<CmpInst>(CurInst)) + continue; + // We don't currently value number ANY inline asm calls. if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) if (CallI->isInlineAsm()) |