[llvm] Reland [SimplifyCFG] Delete the unnecessary range check for small mask operation (PR #70542)
via llvm-commits
llvm-commits at lists.llvm.org
Sat Oct 28 00:44:14 PDT 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Allen (vfdff)
<details>
<summary>Changes</summary>
Fix the compile crash when the default result is not exist for https://github.com/llvm/llvm-project/pull/65835
---
Full diff: https://github.com/llvm/llvm-project/pull/70542.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+22-2)
- (modified) llvm/test/Transforms/SimplifyCFG/switch_mask.ll (+44-14)
``````````diff
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 68b5b1a78a3460e..a9585d2ed963f3a 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6598,9 +6598,8 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
// If the default destination is unreachable, or if the lookup table covers
// all values of the conditional variable, branch directly to the lookup table
// BB. Otherwise, check that the condition is within the case range.
- const bool DefaultIsReachable =
+ bool DefaultIsReachable =
!isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
- const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
// Create the BB that does the lookups.
Module &Mod = *CommonDest->getParent()->getParent();
@@ -6631,6 +6630,27 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
BranchInst *RangeCheckBranch = nullptr;
+ // Grow the table to cover all possible index values to avoid the range check.
+ // It will use the default result to fill in the table hole later, so make
+ // sure it exist.
+ if (UseSwitchConditionAsTableIndex && HasDefaultResults) {
+ ConstantRange CR = computeConstantRange(TableIndex, /* ForSigned */ false);
+ // Grow the table shouldn't have any size impact by checking
+ // WouldFitInRegister.
+ // TODO: Consider growing the table also when it doesn't fit in a register
+ // if no optsize is specified.
+ if (all_of(ResultTypes, [&](const auto &KV) {
+ return SwitchLookupTable::WouldFitInRegister(
+ DL, CR.getUpper().getLimitedValue(), KV.second /* ResultType */);
+ })) {
+ // The default branch is unreachable when we enlarge the lookup table.
+ // Adjust DefaultIsReachable to reuse code path.
+ TableSize = CR.getUpper().getZExtValue();
+ DefaultIsReachable = false;
+ }
+ }
+
+ const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
Builder.CreateBr(LookupBB);
if (DTU)
diff --git a/llvm/test/Transforms/SimplifyCFG/switch_mask.ll b/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
index 8c97a0660d07074..867fbc0c5e9b6c2 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
@@ -8,13 +8,11 @@ define i1 @switch_lookup_with_small_i1(i64 %x) {
; CHECK-LABEL: @switch_lookup_with_small_i1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[AND:%.*]] = and i64 [[X:%.*]], 15
-; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i64 [[AND]], 11
-; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[AND]] to i11
-; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i11 [[SWITCH_CAST]], 1
-; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i11 -1018, [[SWITCH_SHIFTAMT]]
-; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i11 [[SWITCH_DOWNSHIFT]] to i1
-; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[TMP0]], i1 [[SWITCH_MASKED]], i1 false
-; CHECK-NEXT: ret i1 [[TMP1]]
+; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[AND]] to i16
+; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i16 [[SWITCH_CAST]], 1
+; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i16 1030, [[SWITCH_SHIFTAMT]]
+; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i16 [[SWITCH_DOWNSHIFT]] to i1
+; CHECK-NEXT: ret i1 [[SWITCH_MASKED]]
;
entry:
%and = and i64 %x, 15
@@ -37,13 +35,11 @@ define i8 @switch_lookup_with_small_i8(i64 %x) {
; CHECK-LABEL: @switch_lookup_with_small_i8(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[REM:%.*]] = urem i64 [[X:%.*]], 5
-; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i64 [[REM]], 3
-; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[REM]] to i24
-; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i24 [[SWITCH_CAST]], 8
-; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i24 460303, [[SWITCH_SHIFTAMT]]
-; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i24 [[SWITCH_DOWNSHIFT]] to i8
-; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[TMP0]], i8 [[SWITCH_MASKED]], i8 0
-; CHECK-NEXT: ret i8 [[TMP1]]
+; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[REM]] to i40
+; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i40 [[SWITCH_CAST]], 8
+; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i40 460303, [[SWITCH_SHIFTAMT]]
+; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i40 [[SWITCH_DOWNSHIFT]] to i8
+; CHECK-NEXT: ret i8 [[SWITCH_MASKED]]
;
entry:
%rem = urem i64 %x, 5
@@ -107,3 +103,37 @@ lor.end:
%0 = phi i8 [ 15, %sw.bb0 ], [ 6, %sw.bb1 ], [ 7, %sw.bb2 ], [ 0, %default ]
ret i8 %0
}
+
+; Negative test: The default branch is unreachable.
+define i1 @switch_lookup_with_small_i1_unreachable(i32 %x) {
+; CHECK-LABEL: @switch_lookup_with_small_i1_unreachable(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[AND:%.*]] = and i32 [[X:%.*]], 15
+; CHECK-NEXT: ret i1 false
+;
+entry:
+ %and = and i32 %x, 15
+ switch i32 %and, label %default [
+ i32 4, label %phi.end
+ i32 2, label %phi.end
+ i32 10, label %phi.end
+ i32 9, label %phi.end
+ i32 1, label %sw.bb1.i
+ i32 3, label %sw.bb1.i
+ i32 5, label %sw.bb1.i
+ i32 0, label %sw.bb1.i
+ i32 6, label %sw.bb1.i
+ i32 7, label %sw.bb1.i
+ i32 8, label %sw.bb1.i
+ ]
+
+sw.bb1.i: ; preds = %entry, %entry, %entry, %entry, %entry, %entry, %entry
+ br label %phi.end
+
+default: ; preds = %entry
+ unreachable
+
+phi.end: ; preds = %sw.bb1.i, %entry, %entry, %entry, %entry
+ %retval.0.i = phi i1 [ false, %sw.bb1.i ], [ false, %entry ], [ false, %entry ], [ false, %entry ], [ false, %entry ]
+ ret i1 false
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/70542
More information about the llvm-commits
mailing list