fix double pull conflict

Author: glyh

src/riscv/codegen.mbt

@@ -742,7 +742,10 @@ fn CodegenBlock::codegen(self : CodegenBlock) -> Unit {
             let reg_lhs = self.pull_val_i(lhs)
             // NOTE: whenever we pull 2 regs and both of them maybe tmp, 
             // we replace the second tmp with target
-            let reg_rhs = self.pull_val_i(rhs, reg_swap=reg)
+            let reg_rhs = self.pull_val_i(
+              rhs,
+              reg_swap=if reg_lhs == reg_swap { reg } else { reg_swap },
+            )
             match op {
               Add => [Add(reg, reg_lhs, reg_rhs)]
               Sub => [Sub(reg, reg_lhs, reg_rhs)]
@@ -756,7 +759,10 @@ fn CodegenBlock::codegen(self : CodegenBlock) -> Unit {
           bind,
           fn(reg) {
             let reg_lhs = self.pull_val_f(lhs)
-            let reg_rhs = self.pull_val_f(rhs, freg_swap=reg)
+            let reg_rhs = self.pull_val_f(
+              rhs,
+              freg_swap=if reg_lhs == freg_swap { reg } else { freg_swap },
+            )
             match op {
               Add => [FaddD(reg, reg_lhs, reg_rhs)]
               Sub => [FsubD(reg, reg_lhs, reg_rhs)]
@@ -781,7 +787,10 @@ fn CodegenBlock::codegen(self : CodegenBlock) -> Unit {
             self.assign_i(
               bind,
               fn(reg) {
-                let reg_rhs = self.pull_val_i(rhs, reg_swap=reg)
+                let reg_rhs = self.pull_val_i(
+                  rhs,
+                  reg_swap=if reg_lhs == reg_swap { reg } else { reg_swap },
+                )
                 [Xor(reg_swap, reg_lhs, reg_rhs), Seqz(reg, reg_swap)]
               },
             )
@@ -804,7 +813,10 @@ fn CodegenBlock::codegen(self : CodegenBlock) -> Unit {
               bind,
               // HACK: we're using 32bits int so this won't overflow
               fn(reg) {
-                let reg_rhs = self.pull_val_i(rhs, reg_swap=reg)
+                let reg_rhs = self.pull_val_i(
+                  rhs,
+                  reg_swap=if reg_lhs == reg_swap { reg } else { reg_swap },
+                )
                 [
                   Sub(reg, reg_lhs, reg_rhs),
                   Addi(reg, reg, -1),

src/riscv/extern_stub.mbt

@@ -17,7 +17,6 @@ fn collect_externals(cfg : @ssacfg.SsaCfg) -> @hashset.T[Var] {
   }
 
   for item in cfg.blocks {
-    //println("start of \{item.0}: \{out}")
     let (_, blk) = item
     for inst in blk.insts {
       match inst {
@@ -122,13 +121,13 @@ fn generate_stub(cfg : @ssacfg.SsaCfg) -> AssemblyFunction {
     body.append(
       [
         Label(stub_resolved),
-        Comment("call the external function"),
+        Comment("Call the external function"),
         Jalr(T6),
-        Comment("A0 holds result, put continuation as 2nd arg"),
+        Comment("Put continuation at \{kont_reg}"),
         Mv(kont_reg, S1),
-        Comment("fetch continuation address"),
+        Comment("Fetch continuation address"),
         Ld(T1, { base: S1, offset: 0 }),
-        Comment("call continuation"),
+        Comment("Call continuation"),
         Jr(T1),
       ],
     )

src/riscv/reg_allocation.mbt

@@ -31,7 +31,6 @@ fn reg_allocate_on_fn(
   input : @ssacfg.SsaCfg,
   fn_label : Var
 ) -> @hashmap.T[Var, RegRef] {
-  //println("allocation for \{fn_label}")
 
   // generate pre allocation
   let allocation_i : @hashmap.T[Var, Reg] = @hashmap.new()