+ added function TX86AsmOptimizer.Reg1ReadDependsOnReg2, which checks whether

  two registers are independent (taking into account AH vs AL)

git-svn-id: trunk@35991 -

compiler/x86/aoptx86.pas

@@ -40,6 +40,11 @@ unit aoptx86;
       protected
         { checks whether loading a new value in reg1 overwrites the entirety of reg2 }
         function Reg1WriteOverwritesReg2Entirely(reg1, reg2: tregister): boolean;
+        { checks whether reading the value in reg1 depends on the value of reg2. This
+          is very similar to SuperRegisterEquals, except it takes into account that
+          R_SUBH and R_SUBL are independendent (e.g. reading from AL does not
+          depend on the value in AH). }
+        function Reg1ReadDependsOnReg2(reg1, reg2: tregister): boolean;
 
         procedure PostPeepholeOptMov(const p : tai);
 
@@ -263,6 +268,27 @@ unit aoptx86;
       end;
 
 
+    function TX86AsmOptimizer.Reg1ReadDependsOnReg2(reg1, reg2: tregister): boolean;
+      begin
+        if not SuperRegistersEqual(reg1,reg2) then
+          exit(false);
+        if getregtype(reg1)<>R_INTREGISTER then
+          exit(true);  {because SuperRegisterEqual is true}
+        case getsubreg(reg1) of
+          R_SUBL:
+            exit(getsubreg(reg2)<>R_SUBH);
+          R_SUBH:
+            exit(getsubreg(reg2)<>R_SUBL);
+          R_SUBW,
+          R_SUBD,
+          R_SUBQ:
+            exit(true);
+          else
+            internalerror(2017042802);
+        end;
+      end;
+
+
     { allocates register reg between (and including) instructions p1 and p2
       the type of p1 and p2 must not be in SkipInstr
       note that this routine is both called from the peephole optimizer