Skip to content

[InstCombine] Eliminate icmp+zext pairs over phis more aggressively #121767

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Jan 7, 2025
Merged

[InstCombine] Eliminate icmp+zext pairs over phis more aggressively #121767

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
29 changes: 23 additions & 6 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1822,12 +1822,29 @@ Instruction *InstCombinerImpl::foldOpIntoPhi(Instruction &I, PHINode *PN,
continue;
}

// If the only use of phi is comparing it with a constant then we can
// put this comparison in the incoming BB directly after a ucmp/scmp call
// because we know that it will simplify to a single icmp.
const APInt *Ignored;
if (isa<CmpIntrinsic>(InVal) && InVal->hasOneUser() &&
match(&I, m_ICmp(m_Specific(PN), m_APInt(Ignored)))) {
// Handle some cases that can't be fully simplified, but where we know that
// the two instructions will fold into one.
auto WillFold = [&]() {
if (!InVal->hasOneUser())
return false;

// icmp of ucmp/scmp with constant will fold to icmp.
const APInt *Ignored;
if (isa<CmpIntrinsic>(InVal) &&
match(&I, m_ICmp(m_Specific(PN), m_APInt(Ignored))))
return true;

// icmp eq zext(bool), 0 will fold to !bool.
if (isa<ZExtInst>(InVal) &&
cast<ZExtInst>(InVal)->getSrcTy()->isIntOrIntVectorTy(1) &&
match(&I,
m_SpecificICmp(ICmpInst::ICMP_EQ, m_Specific(PN), m_Zero())))
return true;

return false;
};

if (WillFold()) {
OpsToMoveUseToIncomingBB.push_back(i);
NewPhiValues.push_back(nullptr);
continue;
Expand Down
11 changes: 5 additions & 6 deletions llvm/test/Transforms/InstCombine/phi.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2828,13 +2828,13 @@ define i1 @test_zext_icmp_eq_0(i1 %a, i1 %b, i32 %c) {
; CHECK-NEXT: entry:
; CHECK-NEXT: br i1 [[A:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
; CHECK: if:
; CHECK-NEXT: [[B_EXT:%.*]] = zext i1 [[B:%.*]] to i32
; CHECK-NEXT: [[TMP0:%.*]] = xor i1 [[B:%.*]], true
; CHECK-NEXT: br label [[JOIN:%.*]]
; CHECK: else:
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[C:%.*]], 0
; CHECK-NEXT: br label [[JOIN]]
; CHECK: join:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ [[B_EXT]], [[IF]] ], [ [[C:%.*]], [[ELSE]] ]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[PHI]], 0
; CHECK-NEXT: [[CMP:%.*]] = phi i1 [ [[TMP0]], [[IF]] ], [ [[TMP1]], [[ELSE]] ]
; CHECK-NEXT: ret i1 [[CMP]]
;
entry:
Expand Down Expand Up @@ -2916,10 +2916,9 @@ define i1 @test_zext_icmp_eq_0_loop(i1 %c, i1 %b) {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 1, [[ENTRY:%.*]] ], [ [[EXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[X:%.*]] = icmp eq i32 [[PHI]], 0
; CHECK-NEXT: [[X:%.*]] = phi i1 [ false, [[ENTRY:%.*]] ], [ [[TMP0:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[Y:%.*]] = and i1 [[X]], [[B:%.*]]
; CHECK-NEXT: [[EXT]] = zext i1 [[Y]] to i32
; CHECK-NEXT: [[TMP0]] = xor i1 [[Y]], true
; CHECK-NEXT: br i1 [[C:%.*]], label [[LOOP]], label [[EXIT:%.*]]
; CHECK: exit:
; CHECK-NEXT: ret i1 [[X]]
Expand Down
Loading