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[InstCombine] Replace all dominated uses of condition with constants #105510

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Merged
merged 4 commits into from
Sep 1, 2024
Merged

[InstCombine] Replace all dominated uses of condition with constants #105510

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c4d686c
[InstCombine] Use an independent cond for the second branch. NFC.
dtcxzyw Aug 31, 2024
9f69dd6
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Aug 31, 2024
b0b538a
[InstCombine] Replace all dominated uses of condition with constants
dtcxzyw Aug 31, 2024
970a1cd
[InstCombine] Address review comments. NFC.
dtcxzyw Aug 31, 2024
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17 changes: 17 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Expand Up @@ -3705,6 +3705,23 @@ Instruction *InstCombinerImpl::visitBranchInst(BranchInst &BI) {
return nullptr;
}

// Replace all dominated uses of the condition with true/false
if (BI.getSuccessor(0) != BI.getSuccessor(1)) {
for (auto &U : make_early_inc_range(Cond->uses())) {
BasicBlockEdge Edge0(BI.getParent(), BI.getSuccessor(0));
if (DT.dominates(Edge0, U)) {
replaceUse(U, ConstantInt::getTrue(Cond->getType()));
addToWorklist(cast<Instruction>(U.getUser()));
continue;
}
BasicBlockEdge Edge1(BI.getParent(), BI.getSuccessor(1));
if (DT.dominates(Edge1, U)) {
replaceUse(U, ConstantInt::getFalse(Cond->getType()));
addToWorklist(cast<Instruction>(U.getUser()));
}
}
}

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Can we do the same thing with switches?

DC.registerBranch(&BI);
return nullptr;
}
Expand Down
6 changes: 3 additions & 3 deletions llvm/test/Transforms/InstCombine/assume.ll
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Expand Up @@ -485,7 +485,7 @@ define i1 @nonnull3B(ptr %a, i1 %control) {
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]]) [ "nonnull"(ptr [[LOAD]]) ]
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK: not_taken:
; CHECK-NEXT: ret i1 [[CONTROL]]
; CHECK-NEXT: ret i1 false
;
entry:
%load = load ptr, ptr %a
Expand Down Expand Up @@ -513,7 +513,7 @@ define i1 @nonnull3C(ptr %a, i1 %control) {
; CHECK: exit:
; CHECK-NEXT: ret i1 [[CMP2]]
; CHECK: not_taken:
; CHECK-NEXT: ret i1 [[CONTROL]]
; CHECK-NEXT: ret i1 false
;
entry:
%load = load ptr, ptr %a
Expand Down Expand Up @@ -543,7 +543,7 @@ define i1 @nonnull3D(ptr %a, i1 %control) {
; CHECK: exit:
; CHECK-NEXT: ret i1 [[CMP2]]
; CHECK: not_taken:
; CHECK-NEXT: ret i1 [[CONTROL]]
; CHECK-NEXT: ret i1 false
;
entry:
%load = load ptr, ptr %a
Expand Down
96 changes: 96 additions & 0 deletions llvm/test/Transforms/InstCombine/branch.ll
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Expand Up @@ -242,3 +242,99 @@ t:
f:
ret i32 3
}

define i32 @dom_true(i1 %cmp) {
; CHECK-LABEL: @dom_true(
; CHECK-NEXT: br i1 [[CMP:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: ret i32 1
; CHECK: if.else:
; CHECK-NEXT: ret i32 0
;
br i1 %cmp, label %if.then, label %if.else

if.then:
%zext = zext i1 %cmp to i32
ret i32 %zext

if.else:
ret i32 0
}

define i32 @dom_false(i1 %cmp) {
; CHECK-LABEL: @dom_false(
; CHECK-NEXT: br i1 [[CMP:%.*]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
; CHECK: if.then:
; CHECK-NEXT: ret i32 0
; CHECK: if.else:
; CHECK-NEXT: ret i32 0
;
br i1 %cmp, label %if.else, label %if.then

if.then:
%zext = zext i1 %cmp to i32
ret i32 %zext

if.else:
ret i32 0
}

define i32 @dom_true_phi(i1 %cmp) {
; CHECK-LABEL: @dom_true_phi(
; CHECK-NEXT: br i1 [[CMP:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: br label [[IF_END:%.*]]
; CHECK: if.else:
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: [[ZEXT:%.*]] = zext i1 [[CMP]] to i32
; CHECK-NEXT: ret i32 [[ZEXT]]
;
br i1 %cmp, label %if.then, label %if.else

if.then:
br label %if.end

if.else:
br label %if.end

if.end:
%phi = phi i1 [ true, %if.then ], [ %cmp, %if.else ]
%zext = zext i1 %phi to i32
ret i32 %zext
}

; Negative tests

define i32 @same_dest(i1 %cmp) {
; CHECK-LABEL: @same_dest(
; CHECK-NEXT: br i1 false, label [[IF_THEN:%.*]], label [[IF_THEN]]
; CHECK: if.then:
; CHECK-NEXT: [[ZEXT:%.*]] = zext i1 [[CMP:%.*]] to i32
; CHECK-NEXT: ret i32 [[ZEXT]]
;
br i1 %cmp, label %if.then, label %if.then

if.then:
%zext = zext i1 %cmp to i32
ret i32 %zext
}

define i32 @not_dom(i1 %cmp) {
; CHECK-LABEL: @not_dom(
; CHECK-NEXT: br i1 [[CMP:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: br label [[IF_ELSE]]
; CHECK: if.else:
; CHECK-NEXT: [[ZEXT:%.*]] = zext i1 [[CMP]] to i32
; CHECK-NEXT: ret i32 [[ZEXT]]
;
br i1 %cmp, label %if.then, label %if.else

if.then:
br label %if.else

if.else:
%zext = zext i1 %cmp to i32
ret i32 %zext
}
2 changes: 1 addition & 1 deletion llvm/test/Transforms/InstCombine/compare-unescaped.ll
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Expand Up @@ -86,7 +86,7 @@ define i1 @compare_and_call_after() {
; CHECK-NEXT: call void @escape(ptr [[M]])
; CHECK-NEXT: ret i1 true
; CHECK: just_return:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 false
;
%m = call ptr @malloc(i64 24)
%lgp = load ptr, ptr @gp, align 8, !nonnull !0
Expand Down
20 changes: 10 additions & 10 deletions llvm/test/Transforms/InstCombine/icmp-dom.ll
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Expand Up @@ -196,7 +196,7 @@ define i1 @trueblock_cmp_is_false(i32 %x, i32 %y) {
; CHECK: t:
; CHECK-NEXT: ret i1 false
; CHECK: f:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 false
;
entry:
%cmp = icmp sgt i32 %x, %y
Expand All @@ -216,7 +216,7 @@ define i1 @trueblock_cmp_is_false_commute(i32 %x, i32 %y) {
; CHECK: t:
; CHECK-NEXT: ret i1 false
; CHECK: f:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 false
;
entry:
%cmp = icmp eq i32 %x, %y
Expand All @@ -236,7 +236,7 @@ define i1 @trueblock_cmp_is_true(i32 %x, i32 %y) {
; CHECK: t:
; CHECK-NEXT: ret i1 true
; CHECK: f:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 false
;
entry:
%cmp = icmp ult i32 %x, %y
Expand All @@ -256,7 +256,7 @@ define i1 @trueblock_cmp_is_true_commute(i32 %x, i32 %y) {
; CHECK: t:
; CHECK-NEXT: ret i1 true
; CHECK: f:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 false
;
entry:
%cmp = icmp ugt i32 %x, %y
Expand All @@ -271,10 +271,10 @@ f:
define i1 @falseblock_cmp_is_false(i32 %x, i32 %y) {
; CHECK-LABEL: @falseblock_cmp_is_false(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp sle i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: br i1 [[CMP]], label [[T:%.*]], label [[F:%.*]]
; CHECK-NEXT: [[CMP_NOT:%.*]] = icmp sgt i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: br i1 [[CMP_NOT]], label [[F:%.*]], label [[T:%.*]]
; CHECK: t:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 true
; CHECK: f:
; CHECK-NEXT: ret i1 false
;
Expand All @@ -294,7 +294,7 @@ define i1 @falseblock_cmp_is_false_commute(i32 %x, i32 %y) {
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: br i1 [[CMP]], label [[T:%.*]], label [[F:%.*]]
; CHECK: t:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 true
; CHECK: f:
; CHECK-NEXT: ret i1 false
;
Expand All @@ -314,7 +314,7 @@ define i1 @falseblock_cmp_is_true(i32 %x, i32 %y) {
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: br i1 [[CMP]], label [[T:%.*]], label [[F:%.*]]
; CHECK: t:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 true
; CHECK: f:
; CHECK-NEXT: ret i1 true
;
Expand All @@ -334,7 +334,7 @@ define i1 @falseblock_cmp_is_true_commute(i32 %x, i32 %y) {
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: br i1 [[CMP]], label [[T:%.*]], label [[F:%.*]]
; CHECK: t:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 true
; CHECK: f:
; CHECK-NEXT: ret i1 true
;
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/InstCombine/indexed-gep-compares.ll
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Expand Up @@ -292,7 +292,7 @@ define i1 @test7() {
; CHECK-NEXT: [[CMP:%.*]] = phi i1 [ false, [[ENTRY:%.*]] ], [ true, [[BB7]] ]
; CHECK-NEXT: br i1 [[CMP]], label [[BB10:%.*]], label [[BB7]]
; CHECK: bb10:
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 true
;
entry:
br label %bb7
Expand Down
6 changes: 2 additions & 4 deletions llvm/test/Transforms/InstCombine/known-bits.ll
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Expand Up @@ -1664,11 +1664,9 @@ define i64 @pr92084(double %x) {
; CHECK-NEXT: [[CMP:%.*]] = fcmp uno double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN1:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then1:
; CHECK-NEXT: br i1 [[CMP]], label [[IF_ELSE]], label [[IF_THEN2:%.*]]
; CHECK-NEXT: br i1 true, label [[IF_ELSE]], label [[IF_THEN2:%.*]]
; CHECK: if.then2:
; CHECK-NEXT: [[CAST:%.*]] = bitcast double [[X]] to i64
; CHECK-NEXT: [[AND:%.*]] = and i64 [[CAST]], 1
; CHECK-NEXT: ret i64 [[AND]]
; CHECK-NEXT: ret i64 poison
; CHECK: if.else:
; CHECK-NEXT: ret i64 0
;
Expand Down
12 changes: 8 additions & 4 deletions llvm/test/Transforms/InstCombine/phi-known-bits-operand-order.ll
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Expand Up @@ -16,7 +16,8 @@ define void @phi_recurrence_start_first() {
; CHECK-NEXT: br i1 [[COND_V]], label [[IF_THEN:%.*]], label [[WHILE_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[START]] = add nuw nsw i32 [[CELL_0]], 1
; CHECK-NEXT: br i1 [[COND_V]], label [[FOR_COND11:%.*]], label [[FOR_COND26]]
; CHECK-NEXT: [[COND_V2:%.*]] = call i1 @cond()
; CHECK-NEXT: br i1 [[COND_V2]], label [[FOR_COND11:%.*]], label [[FOR_COND26]]
; CHECK: for.cond11:
; CHECK-NEXT: [[I_1:%.*]] = phi i32 [ [[START]], [[IF_THEN]] ], [ [[STEP:%.*]], [[FOR_COND11]] ]
; CHECK-NEXT: [[CMP13:%.*]] = icmp ult i32 [[I_1]], 100
Expand All @@ -37,7 +38,8 @@ while.cond: ; preds = %entry, %for.cond26

if.then: ; preds = %while.cond
%start = add nsw i32 %cell.0, 1
br i1 %cond.v, label %for.cond11, label %for.cond26
%cond.v2 = call i1 @cond()
br i1 %cond.v2, label %for.cond11, label %for.cond26

for.cond11: ; preds = %for.cond11, %if.then
%i.1 = phi i32 [ %start, %if.then ], [ %step, %for.cond11 ]
Expand All @@ -62,7 +64,8 @@ define void @phi_recurrence_step_first() {
; CHECK-NEXT: br i1 [[COND_V]], label [[IF_THEN:%.*]], label [[WHILE_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[START]] = add nuw nsw i32 [[CELL_0]], 1
; CHECK-NEXT: br i1 [[COND_V]], label [[FOR_COND11:%.*]], label [[FOR_COND26]]
; CHECK-NEXT: [[COND_V2:%.*]] = call i1 @cond()
; CHECK-NEXT: br i1 [[COND_V2]], label [[FOR_COND11:%.*]], label [[FOR_COND26]]
; CHECK: for.cond11:
; CHECK-NEXT: [[I_1:%.*]] = phi i32 [ [[STEP:%.*]], [[FOR_COND11]] ], [ [[START]], [[IF_THEN]] ]
; CHECK-NEXT: [[CMP13:%.*]] = icmp ult i32 [[I_1]], 100
Expand All @@ -83,7 +86,8 @@ while.cond: ; preds = %entry, %for.cond26

if.then: ; preds = %while.cond
%start = add nsw i32 %cell.0, 1
br i1 %cond.v, label %for.cond11, label %for.cond26
%cond.v2 = call i1 @cond()
br i1 %cond.v2, label %for.cond11, label %for.cond26

for.cond11: ; preds = %for.cond11, %if.then
%i.1 = phi i32 [ %step, %for.cond11 ], [ %start, %if.then]
Expand Down
16 changes: 8 additions & 8 deletions llvm/test/Transforms/InstCombine/phi.ll
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Expand Up @@ -1543,7 +1543,7 @@ define i1 @phi_knownnonzero_eq_multiuse_oricmp(i32 %n, i32 %s, ptr %P, i32 %val)
; CHECK-NEXT: [[BOOL2:%.*]] = icmp eq i32 [[PHI]], 0
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: cleanup:
; CHECK-NEXT: [[FINAL:%.*]] = phi i1 [ [[CMP1]], [[IF_END]] ], [ [[BOOL2]], [[NEXT]] ]
; CHECK-NEXT: [[FINAL:%.*]] = phi i1 [ false, [[IF_END]] ], [ [[BOOL2]], [[NEXT]] ]
; CHECK-NEXT: ret i1 [[FINAL]]
;
entry:
Expand Down Expand Up @@ -1581,13 +1581,13 @@ define i1 @phi_knownnonzero_ne_multiuse_oricmp_commuted(i32 %n, i32 %s, ptr %P,
; CHECK: if.end:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 1, [[IF_THEN]] ], [ [[N]], [[ENTRY:%.*]] ]
; CHECK-NEXT: [[ORPHI:%.*]] = or i32 [[VAL:%.*]], [[PHI]]
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i32 [[ORPHI]], 0
; CHECK-NEXT: br i1 [[CMP1]], label [[NEXT:%.*]], label [[CLEANUP:%.*]]
; CHECK-NEXT: [[CMP1_NOT:%.*]] = icmp eq i32 [[ORPHI]], 0
; CHECK-NEXT: br i1 [[CMP1_NOT]], label [[CLEANUP:%.*]], label [[NEXT:%.*]]
; CHECK: next:
; CHECK-NEXT: [[BOOL2:%.*]] = icmp ne i32 [[PHI]], 0
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: cleanup:
; CHECK-NEXT: [[FINAL:%.*]] = phi i1 [ [[CMP1]], [[IF_END]] ], [ [[BOOL2]], [[NEXT]] ]
; CHECK-NEXT: [[FINAL:%.*]] = phi i1 [ false, [[IF_END]] ], [ [[BOOL2]], [[NEXT]] ]
; CHECK-NEXT: ret i1 [[FINAL]]
;
entry:
Expand Down Expand Up @@ -1634,7 +1634,7 @@ define i1 @phi_knownnonzero_eq_multiuse_andicmp(i32 %n, i32 %s, ptr %P, i32 %val
; CHECK-NEXT: [[BOOL2:%.*]] = icmp eq i32 [[PHI]], 0
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: cleanup:
; CHECK-NEXT: [[FINAL:%.*]] = phi i1 [ [[CMP1]], [[IF_END]] ], [ [[BOOL2]], [[NEXT]] ]
; CHECK-NEXT: [[FINAL:%.*]] = phi i1 [ false, [[IF_END]] ], [ [[BOOL2]], [[NEXT]] ]
; CHECK-NEXT: ret i1 [[FINAL]]
;
entry:
Expand Down Expand Up @@ -1675,13 +1675,13 @@ define i1 @phi_knownnonzero_ne_multiuse_andicmp(i32 %n, i32 %s, ptr %P, i32 %val
; CHECK: if.end:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ [[SEL]], [[IF_THEN]] ], [ [[N]], [[ENTRY:%.*]] ]
; CHECK-NEXT: [[ANDPHI:%.*]] = and i32 [[PHI]], [[VAL:%.*]]
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i32 [[ANDPHI]], 0
; CHECK-NEXT: br i1 [[CMP1]], label [[NEXT:%.*]], label [[CLEANUP:%.*]]
; CHECK-NEXT: [[CMP1_NOT:%.*]] = icmp eq i32 [[ANDPHI]], 0
; CHECK-NEXT: br i1 [[CMP1_NOT]], label [[CLEANUP:%.*]], label [[NEXT:%.*]]
; CHECK: next:
; CHECK-NEXT: [[BOOL2:%.*]] = icmp ne i32 [[PHI]], 0
; CHECK-NEXT: br label [[CLEANUP]]
; CHECK: cleanup:
; CHECK-NEXT: [[FINAL:%.*]] = phi i1 [ [[CMP1]], [[IF_END]] ], [ [[BOOL2]], [[NEXT]] ]
; CHECK-NEXT: [[FINAL:%.*]] = phi i1 [ false, [[IF_END]] ], [ [[BOOL2]], [[NEXT]] ]
; CHECK-NEXT: ret i1 [[FINAL]]
;
entry:
Expand Down
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