SimplifyCFG: Teach switch generation some patterns that instcombine forms.

This allows us to create switches even if instcombine has munged two of the
incombing compares into one and some bit twiddling. This was motivated by enum
compares that are common in clang.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185632 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 6d12f7a218d50e88378eb8a31d65e6b5b99df014..d8878f2e51220846e16e7e2e630b65a3f66dd9dd 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -40,12 +40,14 @@
 #include "llvm/Support/ConstantRange.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/NoFolder.h"
+#include "llvm/Support/PatternMatch.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include <algorithm>
 #include <map>
 #include <set>
 using namespace llvm;
+using namespace PatternMatch;
 
 static cl::opt<unsigned>
 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
@@ -432,7 +434,24 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
   // If this is an icmp against a constant, handle this as one of the cases.
   if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
     if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
+      Value *RHSVal;
+      ConstantInt *RHSC;
+
       if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
+        // (x & ~2^x) == y --> x == y || x == y|2^x
+        // This undoes a transformation done by instcombine to fuse 2 compares.
+        if (match(ICI->getOperand(0),
+                  m_And(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
+          APInt Not = ~RHSC->getValue();
+          if (Not.isPowerOf2()) {
+            Vals.push_back(C);
+            Vals.push_back(
+                ConstantInt::get(C->getContext(), C->getValue() | Not));
+            UsedICmps++;
+            return RHSVal;
+          }
+        }
+
         UsedICmps++;
         Vals.push_back(C);
         return I->getOperand(0);
@@ -443,6 +462,13 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
       ConstantRange Span =
         ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
 
+      // Shift the range if the compare is fed by an add. This is the range
+      // compare idiom as emitted by instcombine.
+      bool hasAdd =
+          match(I->getOperand(0), m_Add(m_Value(RHSVal), m_ConstantInt(RHSC)));
+      if (hasAdd)
+        Span = Span.subtract(RHSC->getValue());
+
       // If this is an and/!= check then we want to optimize "x ugt 2" into
       // x != 0 && x != 1.
       if (!isEQ)
@@ -455,7 +481,7 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
       for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
         Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
       UsedICmps++;
-      return I->getOperand(0);
+      return hasAdd ? RHSVal : I->getOperand(0);
     }
     return 0;
   }

diff --git a/test/Transforms/SimplifyCFG/switch_create.ll b/test/Transforms/SimplifyCFG/switch_create.ll
index 546cc75f2973b00db9852e6cd0a563d5e16b0a69..9d4e31961f41ff7e61f9e872c1af785180916a64 100644 (file)
--- a/test/Transforms/SimplifyCFG/switch_create.ll
+++ b/test/Transforms/SimplifyCFG/switch_create.ll
@@ -479,3 +479,39 @@ return:
 ; CHECK: ret void
 }
 
+define void @test18(i32 %arg) {
+bb:
+  %tmp = and i32 %arg, -2
+  %tmp1 = icmp eq i32 %tmp, 8
+  %tmp2 = icmp eq i32 %arg, 10
+  %tmp3 = or i1 %tmp1, %tmp2
+  %tmp4 = icmp eq i32 %arg, 11
+  %tmp5 = or i1 %tmp3, %tmp4
+  %tmp6 = icmp eq i32 %arg, 12
+  %tmp7 = or i1 %tmp5, %tmp6
+  br i1 %tmp7, label %bb19, label %bb8
+
+bb8:                                              ; preds = %bb
+  %tmp9 = add i32 %arg, -13
+  %tmp10 = icmp ult i32 %tmp9, 2
+  %tmp11 = icmp eq i32 %arg, 16
+  %tmp12 = or i1 %tmp10, %tmp11
+  %tmp13 = icmp eq i32 %arg, 17
+  %tmp14 = or i1 %tmp12, %tmp13
+  %tmp15 = icmp eq i32 %arg, 18
+  %tmp16 = or i1 %tmp14, %tmp15
+  %tmp17 = icmp eq i32 %arg, 15
+  %tmp18 = or i1 %tmp16, %tmp17
+  br i1 %tmp18, label %bb19, label %bb20
+
+bb19:                                             ; preds = %bb8, %bb
+  tail call void @foo1()
+  br label %bb20
+
+bb20:                                             ; preds = %bb19, %bb8
+  ret void
+
+; CHECK: @test18
+; CHECK: %arg.off = add i32 %arg, -8
+; CHECK: icmp ult i32 %arg.off, 11
+}