From 6fcbe7b3d00ca103d1224e52c246c399dcce4ab8 Mon Sep 17 00:00:00 2001
From: Fabian <copy@copy.sh>
Date: Fri, 4 Nov 2022 12:12:04 -0600
Subject: [PATCH] optimise cmp x, 0; jz

---
 src/rust/codegen.rs | 16 ++++++++++++++--
 src/rust/jit.rs     |  8 ++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/rust/codegen.rs b/src/rust/codegen.rs
index 865e325a..d1ec3066 100644
--- a/src/rust/codegen.rs
+++ b/src/rust/codegen.rs
@@ -348,6 +348,18 @@ fn gen_get_last_result(builder: &mut WasmBuilder, previous_instruction: &Instruc
             dest: InstructionOperandDest::WasmLocal(l),
             opsize: OPSIZE_32,
         } => builder.get_local(&l),
+        Instruction::Cmp {
+            dest: InstructionOperandDest::WasmLocal(l),
+            source,
+            opsize: OPSIZE_32,
+        } => {
+            if source.is_zero() {
+                builder.get_local(&l)
+            }
+            else {
+                builder.load_fixed_i32(global_pointers::last_result as u32)
+            }
+        },
         _ => builder.load_fixed_i32(global_pointers::last_result as u32),
     }
 }
@@ -1582,7 +1594,6 @@ pub fn gen_getzf(ctx: &mut JitContext, negate: ConditionNegate) {
     match &ctx.previous_instruction {
         Instruction::Cmp { .. } | Instruction::Sub { .. } => {
             gen_profiler_stat_increment(ctx.builder, profiler::stat::CONDITION_OPTIMISED);
-            // TODO: Could use local for cmp x, 0
             // TODO: Could use eq(local, local) for cmp x, y
             gen_get_last_result(ctx.builder, &ctx.previous_instruction);
             if negate == ConditionNegate::False {
@@ -1734,7 +1745,8 @@ pub fn gen_getsf(ctx: &mut JitContext) {
             let &opsize = opsize;
             gen_profiler_stat_increment(ctx.builder, profiler::stat::CONDITION_OPTIMISED);
             // TODO:
-            // Could use local for cmp x, 0; test x, x
+            // use local for test x, x
+            // x >= 0 for ConditionNegate::True
             gen_get_last_result(ctx.builder, &ctx.previous_instruction);
             ctx.builder.const_i32(if opsize == OPSIZE_32 {
                 0x8000_0000u32 as i32
diff --git a/src/rust/jit.rs b/src/rust/jit.rs
index 924d513b..18eec8f5 100644
--- a/src/rust/jit.rs
+++ b/src/rust/jit.rs
@@ -244,6 +244,14 @@ pub enum InstructionOperand {
     Immediate(i32),
     Other,
 }
+impl InstructionOperand {
+    pub fn is_zero(&self) -> bool {
+        match self {
+            InstructionOperand::Immediate(0) => true,
+            _ => false,
+        }
+    }
+}
 impl Into<InstructionOperand> for InstructionOperandDest {
     fn into(self: InstructionOperandDest) -> InstructionOperand {
         match self {