[PATCH] D20275: [SimplifyCFG] eliminate switch cases based on known range of switch condition

[Sanjay Patel via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL270222: [SimplifyCFG] eliminate switch cases based on known range of switch condition (authored by spatel).

Changed prior to commit:
  http://reviews.llvm.org/D20275?vs=57856&id=57933#toc

Repository:
  rL LLVM

http://reviews.llvm.org/D20275

Files:
  llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
  llvm/trunk/test/Transforms/SimplifyCFG/switch-masked-bits.ll

Index: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3914,14 +3914,20 @@
   APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
   computeKnownBits(Cond, KnownZero, KnownOne, DL, 0, AC, SI);
 
+  // We can also eliminate cases by determining that their values are outside of
+  // the limited range of the condition based on how many significant (non-sign)
+  // bits are in the condition value.
+  unsigned ExtraSignBits = ComputeNumSignBits(Cond, DL, 0, AC, SI) - 1;
+  unsigned MaxSignificantBitsInCond = Bits - ExtraSignBits;
+
   // Gather dead cases.
   SmallVector<ConstantInt *, 8> DeadCases;
   for (auto &Case : SI->cases()) {
-    if ((Case.getCaseValue()->getValue() & KnownZero) != 0 ||
-        (Case.getCaseValue()->getValue() & KnownOne) != KnownOne) {
+    APInt CaseVal = Case.getCaseValue()->getValue();
+    if ((CaseVal & KnownZero) != 0 || (CaseVal & KnownOne) != KnownOne ||
+        (CaseVal.getMinSignedBits() > MaxSignificantBitsInCond)) {
       DeadCases.push_back(Case.getCaseValue());
-      DEBUG(dbgs() << "SimplifyCFG: switch case '" << Case.getCaseValue()
-                   << "' is dead.\n");
+      DEBUG(dbgs() << "SimplifyCFG: switch case " << CaseVal << " is dead.\n");
     }
   }
 
Index: llvm/trunk/test/Transforms/SimplifyCFG/switch-masked-bits.ll
===================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/switch-masked-bits.ll
+++ llvm/trunk/test/Transforms/SimplifyCFG/switch-masked-bits.ll
@@ -49,14 +49,10 @@
 define i1 @repeated_signbits(i8 %condition) {
 ; CHECK-LABEL: @repeated_signbits(
 ; CHECK:         switch i32
-; CHECK-DAG:     i32 -2147483648, label %a
-; CHECK-DAG:     i32 -129, label %a
 ; CHECK-DAG:     i32 -128, label %a
 ; CHECK-DAG:     i32 -1, label %a
 ; CHECK-DAG:     i32  0, label %a
 ; CHECK-DAG:     i32  127, label %a
-; CHECK-DAG:     i32  128, label %a
-; CHECK-DAG:     i32  2147483647, label %a
 ; CHECK-NEXT:    ]
 ;
 entry:


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D20275.57933.patch
Type: text/x-patch
Size: 2131 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160520/aff5b930/attachment.bin>