[InstCombine] remove unneeded one-use checks for icmp fold

Related folds were added in:
rL125734
...the code comment about register pressure is discussed in
more detail in:
https://bugs.llvm.org/show_bug.cgi?id=2698

But 10 years later, perf testing bzip2 with this change now
shows a slight (0.2% average) improvement on Haswell although
that's probably within test noise.

Given that this is IR canonicalization, we shouldn't be worried
about register pressure though; the backend should be able to
adjust for that as needed.

This is part of solving PR43310 the theoretically right way:
https://bugs.llvm.org/show_bug.cgi?id=43310
...ie, if we don't cripple basic transforms, then we won't
need to add special-case code to detect larger patterns.

rL371940 and rL371981 are related patches in this series.

llvm-svn: 372007

1 files changed, 1 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 5c443faf2f2..e569ae866b5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3697,11 +3697,8 @@ Instruction *InstCombiner::foldICmpBinOp(ICmpInst &I) {
                         C == Op0 ? D : C);
 
   // icmp (A+B), (A+D) -> icmp B, D for equalities or if there is no overflow.
-  // TODO: The one-use checks should not be necessary.
   if (A && C && (A == C || A == D || B == C || B == D) && NoOp0WrapProblem &&
-      NoOp1WrapProblem &&
-      // Try not to increase register pressure.
-      BO0->hasOneUse() && BO1->hasOneUse()) {
+      NoOp1WrapProblem) {
     // Determine Y and Z in the form icmp (X+Y), (X+Z).
     Value *Y, *Z;
     if (A == C) {