SCCP: don't visit instruction that's not in a visited block because block might not be executable

Test case added

Author: dibyendumajumdar

optvm/src/main/java/com/compilerprogramming/ezlang/compiler/SparseConditionalConstantPropagation.java

@@ -65,22 +65,6 @@ public SparseConditionalConstantPropagation constantPropagation(CompiledFunction
         return this;
     }
 
-    @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        sb.append("Flow edges:\n");
-        for (var edge : flowEdges.keySet()) {
-            if (flowEdges.get(edge)) {
-                sb.append(edge).append("=Executable").append("\n");
-            }
-        }
-        sb.append("Lattices:\n");
-        for (var register: valueLattice.getRegisters()) {
-            sb.append(register.name()).append("=").append(valueLattice.get(register)).append("\n");
-        }
-        return sb.toString();
-    }
-
     private void visitBlock(BasicBlock b) {
         for (var phi : b.phis()) {
             visitInstruction(phi);
@@ -109,7 +93,10 @@ private void visitInstruction(Instruction instruction) {
                 SSAEdges.SSADef ssaDef = ssaEdges.get(def);
                 if (ssaDef != null) {
                     for (Instruction use : ssaDef.useList) {
-                        instructionWorkList.push(use);
+                        if (visited.get(use.block.bid))
+                            // Don't visit the instruction if block hasn't been
+                            // visited
+                            instructionWorkList.push(use);
                     }
                 }
             }
@@ -457,6 +444,25 @@ private static boolean evalArith(LatticeElement cell, LatticeElement left, Latti
         return changed;
     }
 
+    @Override
+    public String toString() {
+        StringBuilder sb = new StringBuilder();
+        sb.append("Flow edges:\n");
+        for (var edge : flowEdges.keySet()) {
+            if (flowEdges.get(edge)) {
+                sb.append(edge).append("=Executable").append("\n");
+            }
+            else {
+                sb.append(edge).append("=NOT Executable").append("\n");
+            }
+        }
+        sb.append("Lattices:\n");
+        for (var register: valueLattice.getRegisters()) {
+            sb.append(register.name()).append("=").append(valueLattice.get(register)).append("\n");
+        }
+        return sb.toString();
+    }
+
     /**
      * Maintains a Lattice for each SSA variable - i.e register
      * Initial value of lattice is TOP/Undefined

optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestSCCP.java

@@ -17,6 +17,7 @@ String compileSrc(String src) {
                 var functionBuilder = (CompiledFunction) f.code();
                 new EnterSSA(functionBuilder);
                 BasicBlock.toStr(sb, functionBuilder.entry, new BitSet(), false);
+                //functionBuilder.toDot(sb, false);
                 sb.append(new SparseConditionalConstantPropagation().constantPropagation(functionBuilder).toString());
             }
         }
@@ -53,14 +54,98 @@ func foo()->Int {
     i_1 = 3
     goto  L4
 Flow edges:
+L0->L2=NOT Executable
 L0->L3=Executable
 L4->L1=Executable
+L2->L4=NOT Executable
 L3->L4=Executable
 Lattices:
 i_0=1
 %t1_0=0
 i_1=3
 i_3=3
+""";
+        Assert.assertEquals(expected, actual);
+    }
+
+    // 19.4 in MCIC Appel
+    // Expected results are based on fig 19.13 page 456
+    @Test
+    public void test2() {
+        String src = """
+func foo()->Int {
+    var i = 1
+    var j = 1
+    var k = 0
+    while (k < 100) {
+        if (j < 20) {
+            j = i
+            k = k + 1
+        }
+        else {
+            j = k
+            k = k + 2
+        }
+    }
+    return j
+}
+""";
+        String actual = compileSrc(src);
+        String expected = """
+L0:
+    i_0 = 1
+    j_0 = 1
+    k_0 = 0
+    goto  L2
+L2:
+    k_1 = phi(k_0, k_4)
+    j_1 = phi(j_0, j_4)
+    %t3_0 = k_1<100
+    if %t3_0 goto L3 else goto L4
+L3:
+    %t4_0 = j_1<20
+    if %t4_0 goto L5 else goto L6
+L5:
+    j_3 = i_0
+    %t5_0 = k_1+1
+    k_3 = %t5_0
+    goto  L7
+L7:
+    k_4 = phi(k_3, k_2)
+    j_4 = phi(j_3, j_2)
+    goto  L2
+L6:
+    j_2 = k_1
+    %t6_0 = k_1+2
+    k_2 = %t6_0
+    goto  L7
+L4:
+    ret j_1
+    goto  L1
+L1:
+Flow edges:
+L0->L2=Executable
+L4->L1=Executable
+L2->L3=Executable
+L2->L4=Executable
+L3->L5=Executable
+L7->L2=Executable
+L3->L6=NOT Executable
+L5->L7=Executable
+L6->L7=NOT Executable
+Lattices:
+j_3=1
+%t5_0=varying
+k_3=varying
+k_4=varying
+j_4=1
+i_0=1
+j_0=1
+k_0=0
+k_1=varying
+j_1=1
+%t3_0=varying
+%t4_0=1
 """;
         Assert.assertEquals(expected, actual);
     }