Fix bug in conditional-const-prop when targets of cbr are same (#6936)

Co-authored-by: Joshua Batty <joshpbatty@gmail.com>

Author: vaivaswatha

sway-ir/src/optimize/conditional_constprop.rs

@@ -36,15 +36,16 @@ pub fn ccp(
         if let InstOp::ConditionalBranch {
             cond_value,
             true_block,
-            false_block: _,
+            false_block,
         } = &term.op
         {
             if let Some(Instruction {
                 parent: _,
                 op: InstOp::Cmp(pred, v1, v2),
             }) = cond_value.get_instruction(context)
             {
-                if matches!(pred, Predicate::Equal)
+                if true_block.block != false_block.block
+                    && matches!(pred, Predicate::Equal)
                     && (v1.is_constant(context) ^ v2.is_constant(context)
                         && true_block.block.num_predecessors(context) == 1)
                 {

sway-ir/tests/ccp/ccp1.ir

@@ -26,4 +26,24 @@ script {
         v8 = add v7, p
         ret u64 v8
     }
+
+    // check: fn $ID($(param=$ID): u64) -> u64
+    fn must_not_optimize(p: u64) -> u64 {
+        // check: entry($(p=$ID): u64)
+        entry(p: u64):
+        // check: $(c=$ID) = const u64 100
+        v0 = const u64 100
+        // check: cmp eq $c $param
+        v2 = cmp eq v0 p
+        // check: $ID, $(true_block=$ID)(), $(false_block=$ID)()
+        cbr v2, get_0_block0(), get_0_block0()
+
+        // check: $false_block():
+        get_0_block0():
+        // check: $(one=$ID) = const u64 1
+        v5 = const u64 1
+        // check: $(ID) = add $one, $p
+        v6 = add v5, p
+        ret u64 v6
+    }
 }