[llvm] r222168 - [SimplifyCFG] Make the value type of the hole check bitmask a power-of-2.

[Juergen Ributzka]

Author: ributzka
Date: Mon Nov 17 13:39:56 2014
New Revision: 222168

URL: http://llvm.org/viewvc/llvm-project?rev=222168&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=222168&r1=222167&r2=222168&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Mon Nov 17 13:39:56 2014
@@ -4074,9 +4074,12 @@ static bool SwitchToLookupTable(SwitchIn
                                   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() -

Modified: llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll?rev=222168&r1=222167&r2=222168&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll Mon Nov 17 13:39:56 2014
@@ -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
 }