Reapply r237453 with a fix for the test timeouts.

The test timeouts were due to instcombine fighting itself. Regression test added.
Original log message:

Canonicalize min/max expressions correctly.

This patch introduces a canonical form for min/max idioms where one operand
is extended or truncated. This often happens when the other operand is a
constant. For example:

  %1 = icmp slt i32 %a, i32 0
    %2 = sext i32 %a to i64
      %3 = select i1 %1, i64 %2, i64 0

Would now be canonicalized into:

  %1 = icmp slt i32 %a, i32 0
    %2 = select i1 %1, i32 %a, i32 0
      %3 = sext i32 %2 to i64

This builds upon a patch posted by David Majenemer
(https://www.marc.info/?l=llvm-commits&m=143008038714141&w=2). That pass
passively stopped instcombine from ruining canonical patterns. This
patch additionally actively makes instcombine canonicalize too.

Canonicalization of expressions involving a change in type from int->fp
or fp->int are not yet implemented.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237520 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
James Molloy
2015-05-16 13:10:45 +00:00
parent f01f1c413a
commit bc71c2fd8e
5 changed files with 140 additions and 7 deletions

View File

@@ -435,6 +435,15 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
if (Instruction *Result = commonCastTransforms(CI))
return Result;
// Test if the trunc is the user of a select which is part of a
// minimum or maximum operation. If so, don't do any more simplification.
// Even simplifying demanded bits can break the canonical form of a
// min/max.
Value *LHS, *RHS;
if (SelectInst *SI = dyn_cast<SelectInst>(CI.getOperand(0)))
if (matchSelectPattern(SI, LHS, RHS) != SPF_UNKNOWN)
return nullptr;
// See if we can simplify any instructions used by the input whose sole
// purpose is to compute bits we don't care about.
if (SimplifyDemandedInstructionBits(CI))