improve switch formation to handle small range

comparisons formed by comparisons.  For example,
this:

void foo(unsigned x) {
  if (x == 0 || x == 1 || x == 3 || x == 4 || x == 6) 
    bar();
}

compiles into:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	cmpl	$6, %edi
	ja	LBB0_2
## BB#1:                                ## %entry
	movl	%edi, %eax
	movl	$91, %ecx
	btq	%rax, %rcx
	jb	LBB0_3

instead of:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	cmpl	$2, %edi
	jb	LBB0_4
## BB#1:                                ## %switch.early.test
	cmpl	$6, %edi
	ja	LBB0_3
## BB#2:                                ## %switch.early.test
	movl	%edi, %eax
	movl	$88, %ecx
	btq	%rax, %rcx
	jb	LBB0_4

This catches a bunch of cases in GCC, which look like this:

 %804 = load i32* @which_alternative, align 4, !tbaa !0
 %805 = icmp ult i32 %804, 2
 %806 = icmp eq i32 %804, 3
 %or.cond121 = or i1 %805, %806
 %807 = icmp eq i32 %804, 4
 %or.cond124 = or i1 %or.cond121, %807
 br i1 %or.cond124, label %.thread, label %808

turning this into a range comparison.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122045 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/ConstantRange.h

@@ -54,7 +54,7 @@ public:
   /// @brief Initialize a range of values explicitly. This will assert out if
   /// Lower==Upper and Lower != Min or Max value for its type. It will also
   /// assert out if the two APInt's are not the same bit width.
-  ConstantRange(const APInt& Lower, const APInt& Upper);
+  ConstantRange(const APInt &Lower, const APInt &Upper);
 
   /// makeICmpRegion - Produce the smallest range that contains all values that
   /// might satisfy the comparison specified by Pred when compared to any value

lib/Transforms/Utils/SimplifyCFG.cpp

@@ -28,6 +28,7 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/CFG.h"
+#include "llvm/Support/ConstantRange.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
@@ -305,11 +306,33 @@ 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 (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
+    if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
-      if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
+      if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
         Vals.push_back(C);
         return I->getOperand(0);
       }
+      
+      // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
+      // the set.
+      ConstantRange Span =
+        ConstantRange::makeICmpRegion(ICI->getPredicate(),
+                                      ConstantRange(C->getValue()));
+      
+      // If this is an and/!= check then we want to optimize "x ugt 2" into
+      // x != 0 && x != 1.
+      if (!isEQ)
+        Span = Span.inverse();
+      
+      // If there are a ton of values, we don't want to make a ginormous switch.
+      if (Span.getSetSize().getZExtValue() > 8 || Span.isEmptySet() ||
+          // We don't handle wrapped sets yet.
+          Span.isWrappedSet())
+        return 0;
+      
+      for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
+        Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
+      return I->getOperand(0);
+    }
     return 0;
   }
   

test/Transforms/SimplifyCFG/switch_create.ll

@@ -351,4 +351,73 @@ malformed:
   ret void
 ; CHECK: @test12
 
-}
+}
+
+; test13 - handle switch formation with ult.
+define void @test13(i32 %x) nounwind ssp noredzone {
+entry:
+  %cmp = icmp ult i32 %x, 2
+  br i1 %cmp, label %if.then, label %lor.lhs.false3
+
+lor.lhs.false3:                                   ; preds = %lor.lhs.false
+  %cmp5 = icmp eq i32 %x, 3
+  br i1 %cmp5, label %if.then, label %lor.lhs.false6
+
+lor.lhs.false6:                                   ; preds = %lor.lhs.false3
+  %cmp8 = icmp eq i32 %x, 4
+  br i1 %cmp8, label %if.then, label %lor.lhs.false9
+
+lor.lhs.false9:                                   ; preds = %lor.lhs.false6
+  %cmp11 = icmp eq i32 %x, 6
+  br i1 %cmp11, label %if.then, label %if.end
+
+if.then:                                          ; preds = %lor.lhs.false9, %lor.lhs.false6, %lor.lhs.false3, %lor.lhs.false, %entry
+  call void @foo1() noredzone
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %lor.lhs.false9
+  ret void
+; CHECK: @test13
+; CHECK:  switch i32 %x, label %if.end [
+; CHECK:     i32 6, label %if.then
+; CHECK:     i32 4, label %if.then
+; CHECK:     i32 3, label %if.then
+; CHECK:     i32 1, label %if.then
+; CHECK:     i32 0, label %if.then
+; CHECK:   ]
+}
+
+; test14 - handle switch formation with ult.
+define void @test14(i32 %x) nounwind ssp noredzone {
+entry:
+  %cmp = icmp ugt i32 %x, 2
+  br i1 %cmp, label %lor.lhs.false3, label %if.then
+
+lor.lhs.false3:                                   ; preds = %lor.lhs.false
+  %cmp5 = icmp ne i32 %x, 3
+  br i1 %cmp5, label %lor.lhs.false6, label %if.then
+
+lor.lhs.false6:                                   ; preds = %lor.lhs.false3
+  %cmp8 = icmp ne i32 %x, 4
+  br i1 %cmp8, label %lor.lhs.false9, label %if.then
+
+lor.lhs.false9:                                   ; preds = %lor.lhs.false6
+  %cmp11 = icmp ne i32 %x, 6
+  br i1 %cmp11, label %if.end, label %if.then
+
+if.then:                                          ; preds = %lor.lhs.false9, %lor.lhs.false6, %lor.lhs.false3, %lor.lhs.false, %entry
+  call void @foo1() noredzone
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %lor.lhs.false9
+  ret void
+; CHECK: @test14
+; CHECK:  switch i32 %x, label %if.end [
+; CHECK:     i32 6, label %if.then
+; CHECK:     i32 4, label %if.then
+; CHECK:     i32 3, label %if.then
+; CHECK:     i32 1, label %if.then
+; CHECK:     i32 0, label %if.then
+; CHECK:   ]
+}
+