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

This fold and several others were added in:
rL125734 <https://reviews.llvm.org/rL125734>
...with no explanation for the one-use checks other than the code
comments about register pressure.

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 is a related patch in this series.

llvm-svn: 371981
This commit is contained in:
Sanjay Patel 2019-09-16 12:54:34 +00:00
parent 72b9c4f3bc
commit c5cd808156
2 changed files with 3 additions and 6 deletions
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5
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -3849,10 +3849,7 @@ Instruction *InstCombiner::foldICmpBinOp(ICmpInst &I) {
return new ICmpInst(Pred, A, C);
// icmp (A-B), (A-D) -> icmp D, B for equalities or if there is no overflow.
// TODO: The one-use checks should not be necessary.
if (A && C && A == C && NoOp0WrapProblem && NoOp1WrapProblem &&
// Try not to increase register pressure.
BO0->hasOneUse() && BO1->hasOneUse())
if (A && C && A == C && NoOp0WrapProblem && NoOp1WrapProblem)
return new ICmpInst(Pred, D, B);
// icmp (0-X) < cst --> x > -cst

4
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -734,7 +734,7 @@ define i1 @test37_extra_uses(i32 %x, i32 %y, i32 %z) {
; CHECK-NEXT: call void @foo(i32 [[LHS]])
; CHECK-NEXT: [[RHS:%.*]] = sub nsw i32 [[X]], [[Z:%.*]]
; CHECK-NEXT: call void @foo(i32 [[RHS]])
; CHECK-NEXT: [[C:%.*]] = icmp sgt i32 [[LHS]], [[RHS]]
; CHECK-NEXT: [[C:%.*]] = icmp sgt i32 [[Z]], [[Y]]
; CHECK-NEXT: ret i1 [[C]]
;
%lhs = sub nsw i32 %x, %y
@ -763,7 +763,7 @@ define i1 @test38_extra_uses(i32 %x, i32 %y, i32 %z) {
; CHECK-NEXT: call void @foo(i32 [[LHS]])
; CHECK-NEXT: [[RHS:%.*]] = sub nuw i32 [[X]], [[Z:%.*]]
; CHECK-NEXT: call void @foo(i32 [[RHS]])
; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[LHS]], [[RHS]]
; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[Z]], [[Y]]
; CHECK-NEXT: ret i1 [[C]]
;
%lhs = sub nuw i32 %x, %y