Add support for "switch" statements.

Switches with both uniform and varying "switch" expressions are
supported.  Switch statements with varying expressions and very
large numbers of labels may not perform well; some issues to be
filed shortly will track opportunities for improving these.

ctx.h

@@ -187,6 +187,45 @@ public:
         previous iteration. */
     void RestoreContinuedLanes();
 
+    /** Indicates that code generation for a "switch" statement is about to
+        start.  isUniform indicates whether the "switch" value is uniform,
+        and bbAfterSwitch gives the basic block immediately following the
+        "switch" statement.  (For example, if the switch condition is
+        uniform, we jump here upon executing a "break" statement.) */
+    void StartSwitch(bool isUniform, llvm::BasicBlock *bbAfterSwitch);
+    /** Indicates the end of code generation for a "switch" statement. */
+    void EndSwitch();
+
+    /** Emits code for a "switch" statement in the program.
+        @param expr         Gives the value of the expression after the "switch"
+        @param defaultBlock Basic block to execute for the "default" case.  This
+                            should be NULL if there is no "default" label inside
+                            the switch.
+        @param caseBlocks   vector that stores the mapping from label values
+                            after "case" statements to basic blocks corresponding
+                            to the "case" labels.
+        @param nextBlocks   For each basic block for a "case" or "default" 
+                            label, this gives the basic block for the 
+                            immediately-following "case" or "default" label (or
+                            the basic block after the "switch" statement for the
+                            last label.)
+    */
+    void SwitchInst(llvm::Value *expr, llvm::BasicBlock *defaultBlock,
+                    const std::vector<std::pair<int, llvm::BasicBlock *> > &caseBlocks,
+                    const std::map<llvm::BasicBlock *, llvm::BasicBlock *> &nextBlocks);
+
+    /** Generates code for a "default" label after a "switch" statement.
+        The checkMask parameter indicates whether additional code should be
+        generated to check to see if the execution mask is all off after
+        the default label (in which case a jump to the following label will
+        be issued. */
+    void EmitDefaultLabel(bool checkMask, SourcePos pos);
+
+    /** Generates code for a "case" label after a "switch" statement.  See
+        the documentation for EmitDefaultLabel() for discussion of the
+        checkMask parameter. */
+    void EmitCaseLabel(int value, bool checkMask, SourcePos pos);
+
     /** Returns the current number of nested levels of 'varying' control
         flow */
     int VaryingCFDepth() const;
@@ -221,6 +260,10 @@ public:
         i1 value that indicates if all of the mask lanes are on. */
     llvm::Value *All(llvm::Value *mask);
 
+    /** Given a boolean mask value of type LLVMTypes::MaskType, return an
+        i1 value that indicates if all of the mask lanes are off. */
+    llvm::Value *None(llvm::Value *mask);
+
     /** Given a boolean mask value of type LLVMTypes::MaskType, return an
         i32 value wherein the i'th bit is on if and only if the i'th lane
         of the mask is on. */
@@ -492,10 +535,10 @@ private:
         the loop. */
     llvm::Value *loopMask;
 
-    /** If currently in a loop body, this is a pointer to memory to store a
-        mask value that represents which of the lanes have executed a
-        'break' statement.  If we're not in a loop body, this should be
-        NULL. */
+    /** If currently in a loop body or switch statement, this is a pointer
+        to memory to store a mask value that represents which of the lanes
+        have executed a 'break' statement.  If we're not in a loop body or
+        switch, this should be NULL. */
     llvm::Value *breakLanesPtr;
 
     /** Similar to breakLanesPtr, if we're inside a loop, this is a pointer
@@ -503,16 +546,42 @@ private:
         'continue' statement. */
     llvm::Value *continueLanesPtr;
 
-    /** If we're inside a loop, this gives the basic block immediately
-        after the current loop, which we will jump to if all of the lanes
-        have executed a break statement or are otherwise done with the
-        loop. */
+    /** If we're inside a loop or switch statement, this gives the basic
+        block immediately after the current loop or switch, which we will
+        jump to if all of the lanes have executed a break statement or are
+        otherwise done with it. */
     llvm::BasicBlock *breakTarget;
 
     /** If we're inside a loop, this gives the block to jump to if all of
         the running lanes have executed a 'continue' statement. */
     llvm::BasicBlock *continueTarget;
 
+    /** @name Switch statement state
+
+        These variables store various state that's active when we're
+        generating code for a switch statement.  They should all be NULL
+        outside of a switch.
+        @{
+    */
+
+    /** The value of the expression used to determine which case in the
+        statements after the switch to execute. */
+    llvm::Value *switchExpr;
+
+    /** Map from case label numbers to the basic block that will hold code
+        for that case. */
+    const std::vector<std::pair<int, llvm::BasicBlock *> > *caseBlocks;
+
+    /** The basic block of code to run for the "default" label in the
+        switch statement. */
+    llvm::BasicBlock *defaultBlock;
+
+    /** For each basic block for the code for cases (and the default label,
+        if present), this map gives the basic block for the immediately
+        following case/default label. */
+    const std::map<llvm::BasicBlock *, llvm::BasicBlock *> *nextBlocks;
+    /** @} */
+
     /** A pointer to memory that records which of the program instances
         have executed a 'return' statement (and are thus really truly done
         running any more instructions in this functions. */
@@ -556,7 +625,7 @@ private:
 
     llvm::Value *pointerVectorToVoidPointers(llvm::Value *value);
     static void addGSMetadata(llvm::Value *inst, SourcePos pos);
-    bool ifsInLoopAllUniform() const;
+    bool ifsInCFAllUniform(int cfType) const;
     void jumpIfAllLoopLanesAreDone(llvm::BasicBlock *target);
     llvm::Value *emitGatherCallback(llvm::Value *lvalue, llvm::Value *retPtr);
 
@@ -564,6 +633,12 @@ private:
                                  const Type *ptrType);
 
     void restoreMaskGivenReturns(llvm::Value *oldMask);
+    void addSwitchMaskCheck(llvm::Value *mask);
+    bool inUniformSwitch() const;
+    bool inVaryingSwitch() const;
+    llvm::Value *getMaskAtSwitchEntry();
+
+    CFInfo *popCFState();
 
     void scatter(llvm::Value *value, llvm::Value *ptr, const Type *ptrType, 
                  llvm::Value *mask);