[SimplifyCFG] Make the value type of the hole check bitmask a power-of-2.

When converting a switch to a lookup table we might have to generate a bitmaks
to encode and check for holes in the original switch statement.

The type of this mask depends on the number of switch statements, which can
result in illegal types for pretty much all architectures.

To avoid unnecessary type legalization and help FastISel this commit increases
the size of the bitmask to next power-of-2 value when necessary.

This fixes rdar://problem/18984639.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222168 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index a8a97f0e25ce07b7c6ebf0b99396628bda563c8a..e3bdd6066be091b9e0f3a9c0c89000b58d314bbf 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4074,9 +4074,12 @@ static bool SwitchToLookupTable(SwitchInst *SI,
                                   CommonDest->getParent(),
                                   CommonDest);
 
+    // Make the mask's bitwidth at least 8bit and a power-of-2 to avoid
+    // unnecessary illegal types.
+    uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL));
+    APInt MaskInt(TableSizePowOf2, 0);
+    APInt One(TableSizePowOf2, 1);
     // Build bitmask; fill in a 1 bit for every case.
-    APInt MaskInt(TableSize, 0);
-    APInt One(TableSize, 1);
     const ResultListTy &ResultList = ResultLists[PHIs[0]];
     for (size_t I = 0, E = ResultList.size(); I != E; ++I) {
       uint64_t Idx = (ResultList[I].first->getValue() -

diff --git a/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
index b9f0e49cbe6b7e90602a7528ee0de9a159a919f7..fc22e7eb45548c357753d57e54390c8a0230672c 100644 (file)
--- a/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -856,10 +856,10 @@ return:
 ; CHECK: entry:
 ; CHECK: br i1 %{{.*}}, label %switch.hole_check, label %sw.default
 ; CHECK: switch.hole_check:
-; CHECK-NEXT: %switch.maskindex = trunc i32 %switch.tableidx to i6
-; CHECK-NEXT: %switch.shifted = lshr i6 -17, %switch.maskindex
+; CHECK-NEXT: %switch.maskindex = trunc i32 %switch.tableidx to i8
+; CHECK-NEXT: %switch.shifted = lshr i8 47, %switch.maskindex
 ; The mask is binary 101111.
-; CHECK-NEXT: %switch.lobit = trunc i6 %switch.shifted to i1
+; CHECK-NEXT: %switch.lobit = trunc i8 %switch.shifted to i1
 ; CHECK-NEXT: br i1 %switch.lobit, label %switch.lookup, label %sw.default
 ; CHECK-NOT: switch i32
 }