[llvm] r185632 - SimplifyCFG: Teach switch generation some patterns that instcombine forms.

[Benjamin Kramer]

Author: d0k
Date: Thu Jul  4 09:22:02 2013
New Revision: 185632

URL: http://llvm.org/viewvc/llvm-project?rev=185632&view=rev
Log:
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.

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

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=185632&r1=185631&r2=185632&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Thu Jul  4 09:22:02 2013
@@ -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::ve
   // 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::ve
       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::ve
       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;
   }

Modified: llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll?rev=185632&r1=185631&r2=185632&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll Thu Jul  4 09:22:02 2013
@@ -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
+}