[llvm] 338fd8b - [SimplifyCFG] Transform switch to select when common bits uniquely identify one case (#145233)
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llvm-commits at lists.llvm.org
Wed Jul 2 09:16:16 PDT 2025
Author: Gábor Spaits
Date: 2025-07-02T18:16:12+02:00
New Revision: 338fd8b12ce67eff73ed0a5c2174bee077fcbcbe
URL: https://github.com/llvm/llvm-project/commit/338fd8b12ce67eff73ed0a5c2174bee077fcbcbe
DIFF: https://github.com/llvm/llvm-project/commit/338fd8b12ce67eff73ed0a5c2174bee077fcbcbe.diff
LOG: [SimplifyCFG] Transform switch to select when common bits uniquely identify one case (#145233)
Fix #141753 .
This patch introduces a new check, that tries to decide if the
conjunction of all the values uniquely identify the accepted values by
the switch.
Added:
Modified:
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 147d2060e8509..a75f29000ca18 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6198,7 +6198,7 @@ static bool initializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
// TODO: Handle switches with more than 2 cases that map to the same result.
static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
Constant *DefaultResult, Value *Condition,
- IRBuilder<> &Builder) {
+ IRBuilder<> &Builder, const DataLayout &DL) {
// If we are selecting between only two cases transform into a simple
// select or a two-way select if default is possible.
// Example:
@@ -6234,10 +6234,33 @@ static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
// case 0,2,8,10 -> Cond & 0b1..0101 == 0 ? result : default
if (isPowerOf2_32(CaseCount)) {
ConstantInt *MinCaseVal = CaseValues[0];
- // Find mininal value.
- for (auto *Case : CaseValues)
+ // If there are bits that are set exclusively by CaseValues, we
+ // can transform the switch into a select if the conjunction of
+ // all the values uniquely identify CaseValues.
+ APInt AndMask = APInt::getAllOnes(MinCaseVal->getBitWidth());
+
+ // Find the minimum value and compute the and of all the case values.
+ for (auto *Case : CaseValues) {
if (Case->getValue().slt(MinCaseVal->getValue()))
MinCaseVal = Case;
+ AndMask &= Case->getValue();
+ }
+ KnownBits Known = computeKnownBits(Condition, DL);
+
+ if (!AndMask.isZero() && Known.getMaxValue().uge(AndMask)) {
+ // Compute the number of bits that are free to vary.
+ unsigned FreeBits = Known.countMaxActiveBits() - AndMask.popcount();
+
+ // Check if the number of values covered by the mask is equal
+ // to the number of cases.
+ if (FreeBits == Log2_32(CaseCount)) {
+ Value *And = Builder.CreateAnd(Condition, AndMask);
+ Value *Cmp = Builder.CreateICmpEQ(
+ And, Constant::getIntegerValue(And->getType(), AndMask));
+ return Builder.CreateSelect(Cmp, ResultVector[0].first,
+ DefaultResult);
+ }
+ }
// Mark the bits case number touched.
APInt BitMask = APInt::getZero(MinCaseVal->getBitWidth());
@@ -6325,7 +6348,7 @@ static bool trySwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
assert(PHI != nullptr && "PHI for value select not found");
Builder.SetInsertPoint(SI);
Value *SelectValue =
- foldSwitchToSelect(UniqueResults, DefaultResult, Cond, Builder);
+ foldSwitchToSelect(UniqueResults, DefaultResult, Cond, Builder, DL);
if (!SelectValue)
return false;
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll b/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
index 50998e447b71d..fe2e897125eb8 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
@@ -309,3 +309,444 @@ end:
%t0 = phi i8 [ 42, %case1 ], [ 42, %case2 ], [ 44, %case3 ], [ 44, %case4 ]
ret i8 %t0
}
+
+define i1 @no_range(i8 %f) {
+; CHECK-LABEL: @no_range(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = and i8 [[F:%.*]], 60
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 60
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 60, label %bb2
+ i8 61, label %bb2
+ i8 62, label %bb2
+ i8 63, label %bb2
+ i8 124, label %bb2
+ i8 188, label %bb2
+ i8 252, label %bb2
+ i8 189, label %bb2
+ i8 190, label %bb2
+ i8 191, label %bb2
+ i8 125, label %bb2
+ i8 126, label %bb2
+ i8 127, label %bb2
+ i8 253, label %bb2
+ i8 254, label %bb2
+ i8 255, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @negative_no_range(i8 %f) {
+; CHECK-LABEL: @negative_no_range(
+; CHECK-NEXT: switch i8 [[F:%.*]], label [[BB3:%.*]] [
+; CHECK-NEXT: i8 52, label [[BB2:%.*]]
+; CHECK-NEXT: i8 61, label [[BB2]]
+; CHECK-NEXT: i8 62, label [[BB2]]
+; CHECK-NEXT: i8 63, label [[BB2]]
+; CHECK-NEXT: i8 124, label [[BB2]]
+; CHECK-NEXT: i8 -68, label [[BB2]]
+; CHECK-NEXT: i8 -4, label [[BB2]]
+; CHECK-NEXT: i8 -67, label [[BB2]]
+; CHECK-NEXT: i8 -66, label [[BB2]]
+; CHECK-NEXT: i8 -65, label [[BB2]]
+; CHECK-NEXT: i8 125, label [[BB2]]
+; CHECK-NEXT: i8 126, label [[BB2]]
+; CHECK-NEXT: i8 127, label [[BB2]]
+; CHECK-NEXT: i8 -3, label [[BB2]]
+; CHECK-NEXT: i8 -2, label [[BB2]]
+; CHECK-NEXT: i8 -1, label [[BB2]]
+; CHECK-NEXT: ]
+; CHECK: bb2:
+; CHECK-NEXT: br label [[BB3]]
+; CHECK: bb3:
+; CHECK-NEXT: [[_0_SROA_0_0:%.*]] = phi i1 [ true, [[BB2]] ], [ false, [[TMP0:%.*]] ]
+; CHECK-NEXT: ret i1 [[_0_SROA_0_0]]
+;
+ switch i8 %f, label %bb1 [
+ i8 52, label %bb2
+ i8 61, label %bb2
+ i8 62, label %bb2
+ i8 63, label %bb2
+ i8 124, label %bb2
+ i8 188, label %bb2
+ i8 252, label %bb2
+ i8 189, label %bb2
+ i8 190, label %bb2
+ i8 191, label %bb2
+ i8 125, label %bb2
+ i8 126, label %bb2
+ i8 127, label %bb2
+ i8 253, label %bb2
+ i8 254, label %bb2
+ i8 255, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+; Using ranges.
+
+define i1 @range0to4odd(i8 range(i8 0, 4) %f) {
+; CHECK-LABEL: @range0to4odd(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = and i8 [[F:%.*]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 1
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 1, label %bb2
+ i8 3, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @range1to4odd(i8 range(i8 1, 4) %f) {
+; CHECK-LABEL: @range1to4odd(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = and i8 [[F:%.*]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 1
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 1, label %bb2
+ i8 3, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @range0to8odd(i8 range(i8 0, 8) %f) {
+; CHECK-LABEL: @range0to8odd(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = and i8 [[F:%.*]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 1
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 1, label %bb2
+ i8 3, label %bb2
+ i8 5, label %bb2
+ i8 7, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @range0to8most_significant_bit(i8 range(i8 0, 8) %f) {
+; CHECK-LABEL: @range0to8most_significant_bit(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = and i8 [[F:%.*]], 4
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 4
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 4, label %bb2
+ i8 5, label %bb2
+ i8 6, label %bb2
+ i8 7, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @range0to15_middle_two_bits(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @range0to15_middle_two_bits(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = and i8 [[F:%.*]], 6
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 6
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 6, label %bb2
+ i8 7, label %bb2
+ i8 14, label %bb2
+ i8 15, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @negative_range0to15(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @negative_range0to15(
+; CHECK-NEXT: switch i8 [[F:%.*]], label [[BB3:%.*]] [
+; CHECK-NEXT: i8 6, label [[BB2:%.*]]
+; CHECK-NEXT: i8 7, label [[BB2]]
+; CHECK-NEXT: i8 14, label [[BB2]]
+; CHECK-NEXT: ]
+; CHECK: bb2:
+; CHECK-NEXT: br label [[BB3]]
+; CHECK: bb3:
+; CHECK-NEXT: [[_0_SROA_0_0:%.*]] = phi i1 [ true, [[BB2]] ], [ false, [[TMP0:%.*]] ]
+; CHECK-NEXT: ret i1 [[_0_SROA_0_0]]
+;
+ switch i8 %f, label %bb1 [
+ i8 6, label %bb2
+ i8 7, label %bb2
+ i8 14, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @negative_range0to15_pow_2(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @negative_range0to15_pow_2(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = sub i8 [[F:%.*]], 6
+; CHECK-NEXT: [[SWITCH_AND:%.*]] = and i8 [[TMP0]], -2
+; CHECK-NEXT: [[SWITCH_SELECTCMP:%.*]] = icmp eq i8 [[SWITCH_AND]], 0
+; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP1]]
+;
+ switch i8 %f, label %bb1 [
+ i8 6, label %bb2
+ i8 7, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @negative_range0to5even(i8 range(i8 0, 5) %f) {
+; CHECK-LABEL: @negative_range0to5even(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = sub i8 [[F:%.*]], 2
+; CHECK-NEXT: [[SWITCH_AND:%.*]] = and i8 [[TMP0]], -3
+; CHECK-NEXT: [[SWITCH_SELECTCMP:%.*]] = icmp eq i8 [[SWITCH_AND]], 0
+; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP1]]
+;
+ switch i8 %f, label %bb1 [
+ i8 2, label %bb2
+ i8 4, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @range0to15_corner_case(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @range0to15_corner_case(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[COND:%.*]] = icmp eq i8 [[F:%.*]], 15
+; CHECK-NEXT: [[DOT:%.*]] = select i1 [[COND]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[DOT]]
+;
+ switch i8 %f, label %bb1 [
+ i8 15, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @negative_range0to15_corner_case(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @negative_range0to15_corner_case(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[SWITCH_SELECTCMP_CASE1:%.*]] = icmp eq i8 [[F:%.*]], 15
+; CHECK-NEXT: [[SWITCH_SELECTCMP_CASE2:%.*]] = icmp eq i8 [[F]], 8
+; CHECK-NEXT: [[SWITCH_SELECTCMP:%.*]] = or i1 [[SWITCH_SELECTCMP_CASE1]], [[SWITCH_SELECTCMP_CASE2]]
+; CHECK-NEXT: [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP0]]
+;
+ switch i8 %f, label %bb1 [
+ i8 15, label %bb2
+ i8 8, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+; Out of range scenarios. Check if the cases, that have a value out of range
+; are eliminated and the optimization is performed.
+
+define i1 @range0to15_out_of_range_non_prime(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @range0to15_out_of_range_non_prime(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = and i8 [[F:%.*]], 6
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 6
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 6, label %bb2
+ i8 7, label %bb2
+ i8 14, label %bb2
+ i8 15, label %bb2
+ i8 22, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @range0to15_out_of_range_non_prime_more(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @range0to15_out_of_range_non_prime_more(
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[TMP0:%.*]] = and i8 [[F:%.*]], 6
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 6
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 6, label %bb2
+ i8 7, label %bb2
+ i8 14, label %bb2
+ i8 15, label %bb2
+ i8 22, label %bb2
+ i8 23, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @negative_range0to15_out_of_range_non_prime(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @negative_range0to15_out_of_range_non_prime(
+; CHECK-NEXT: switch i8 [[F:%.*]], label [[BB3:%.*]] [
+; CHECK-NEXT: i8 6, label [[BB2:%.*]]
+; CHECK-NEXT: i8 14, label [[BB2]]
+; CHECK-NEXT: i8 15, label [[BB2]]
+; CHECK-NEXT: ]
+; CHECK: bb2:
+; CHECK-NEXT: br label [[BB3]]
+; CHECK: bb3:
+; CHECK-NEXT: [[TMP2:%.*]] = phi i1 [ true, [[BB2]] ], [ false, [[TMP0:%.*]] ]
+; CHECK-NEXT: ret i1 [[TMP2]]
+;
+ switch i8 %f, label %bb1 [
+ i8 6, label %bb2
+ i8 14, label %bb2
+ i8 15, label %bb2
+ i8 23, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @negative_range0to15_out_of_range(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @negative_range0to15_out_of_range(
+; CHECK-NEXT: switch i8 [[F:%.*]], label [[BB3:%.*]] [
+; CHECK-NEXT: i8 6, label [[BB2:%.*]]
+; CHECK-NEXT: i8 7, label [[BB2]]
+; CHECK-NEXT: i8 14, label [[BB2]]
+; CHECK-NEXT: ]
+; CHECK: bb2:
+; CHECK-NEXT: br label [[BB3]]
+; CHECK: bb3:
+; CHECK-NEXT: [[_0_SROA_0_0:%.*]] = phi i1 [ true, [[BB2]] ], [ false, [[TMP0:%.*]] ]
+; CHECK-NEXT: ret i1 [[_0_SROA_0_0]]
+;
+ switch i8 %f, label %bb1 [
+ i8 6, label %bb2
+ i8 7, label %bb2
+ i8 14, label %bb2
+ i8 150, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
+
+define i1 @negative_range0to15_all_out_of_range(i8 range(i8 0, 16) %f) {
+; CHECK-LABEL: @negative_range0to15_all_out_of_range(
+; CHECK-NEXT: bb1:
+; CHECK-NEXT: ret i1 false
+;
+ switch i8 %f, label %bb1 [
+ i8 22, label %bb2
+ i8 23, label %bb2
+ i8 30, label %bb2
+ i8 31, label %bb2
+ ]
+bb1:
+ br label %bb3
+bb2:
+ br label %bb3
+bb3:
+ %phi = phi i1 [ false, %bb1 ], [ true, %bb2 ]
+ ret i1 %phi
+}
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