From 67ae89e4177df755503660f088366bf22ded1fbf Mon Sep 17 00:00:00 2001
From: "kmillikin@chromium.org"
 <kmillikin@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Fri, 31 Oct 2008 11:55:06 +0000
Subject: [PATCH] Simplify the way we materialize boolean values that are not
 yet pushed on the stack frame. Review URL:
 http://codereview.chromium.org/8764

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@671 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/codegen-arm.cc  | 36 +++++++++++++++---------------------
 src/codegen-ia32.cc | 37 +++++++++++++++----------------------
 2 files changed, 30 insertions(+), 43 deletions(-)

diff --git a/src/codegen-arm.cc b/src/codegen-arm.cc
index 35522b19ad..b39180ed82 100644
--- a/src/codegen-arm.cc
+++ b/src/codegen-arm.cc
@@ -359,47 +359,41 @@ void CodeGenerator::Load(Expression* x, TypeofState typeof_state) {
   Label false_target;
   LoadCondition(x, typeof_state, &true_target, &false_target, false);
 
+  // Materialize boolean values on the stack frame if necessary.
   if (has_cc()) {
-    // convert cc_reg_ into a bool
-    Label loaded, materialize_true;
-    __ b(cc_reg_, &materialize_true);
+    // The value we want is in the cc register.  Since complicated
+    // conditions can require more than one test, there may also be branches
+    // to true_target and false_target.
+    Label loaded;
+    __ b(cc_reg_, &true_target);
+    __ bind(&false_target);
     __ mov(r0, Operand(Factory::false_value()));
     __ push(r0);
     __ b(&loaded);
-    __ bind(&materialize_true);
+    __ bind(&true_target);
     __ mov(r0, Operand(Factory::true_value()));
     __ push(r0);
     __ bind(&loaded);
     cc_reg_ = al;
-  }
+  } else {
+    // Optimization of boolean-valued expressions whose value is statically
+    // known may have generated an unconditional jump to either of the
+    // targets (but not both) and failed to leave a value in either the cc
+    // register or on top of the frame.
+    ASSERT(!(true_target.is_linked() && false_target.is_linked()));
 
-  if (true_target.is_linked() || false_target.is_linked()) {
-    // we have at least one condition value
-    // that has been "translated" into a branch,
-    // thus it needs to be loaded explicitly again
-    Label loaded;
-    __ b(&loaded);  // don't lose current TOS
-    bool both = true_target.is_linked() && false_target.is_linked();
-    // reincarnate "true", if necessary
     if (true_target.is_linked()) {
       __ bind(&true_target);
       __ mov(r0, Operand(Factory::true_value()));
       __ push(r0);
     }
-    // if both "true" and "false" need to be reincarnated,
-    // jump across code for "false"
-    if (both)
-      __ b(&loaded);
-    // reincarnate "false", if necessary
+
     if (false_target.is_linked()) {
       __ bind(&false_target);
       __ mov(r0, Operand(Factory::false_value()));
       __ push(r0);
     }
-    // everything is loaded at this point
-    __ bind(&loaded);
   }
-  ASSERT(!has_cc());
 }
 
 
diff --git a/src/codegen-ia32.cc b/src/codegen-ia32.cc
index eaac989061..d53e22548d 100644
--- a/src/codegen-ia32.cc
+++ b/src/codegen-ia32.cc
@@ -474,44 +474,37 @@ void CodeGenerator::Load(Expression* x, TypeofState typeof_state) {
   Label false_target;
   LoadCondition(x, typeof_state, &true_target, &false_target, false);
 
+  // Materialize boolean values on the stack frame if necessary.
   if (has_cc()) {
-    // convert cc_reg_ into a bool
-
-    Label loaded, materialize_true;
-    __ j(cc_reg_, &materialize_true);
+    // The value we want is in the cc register.  Since complicated
+    // conditions can require more than one test, there may also be branches
+    // to true_target and false_target.
+    Label loaded;
+    __ j(cc_reg_, &true_target);
+    __ bind(&false_target);
     frame_->Push(Immediate(Factory::false_value()));
     __ jmp(&loaded);
-    __ bind(&materialize_true);
+    __ bind(&true_target);
     frame_->Push(Immediate(Factory::true_value()));
     __ bind(&loaded);
     cc_reg_ = no_condition;
-  }
+  } else {
+    // Optimization of boolean-valued expressions whose value is statically
+    // known may have generated an unconditional jump to either of the
+    // targets (but not both) and failed to leave a value in either the cc
+    // register or on top of the frame.
+    ASSERT(!(true_target.is_linked() && false_target.is_linked()));
 
-  if (true_target.is_linked() || false_target.is_linked()) {
-    // we have at least one condition value
-    // that has been "translated" into a branch,
-    // thus it needs to be loaded explicitly again
-    Label loaded;
-    __ jmp(&loaded);  // don't lose current TOS
-    bool both = true_target.is_linked() && false_target.is_linked();
-    // reincarnate "true", if necessary
     if (true_target.is_linked()) {
       __ bind(&true_target);
       frame_->Push(Immediate(Factory::true_value()));
     }
-    // if both "true" and "false" need to be reincarnated,
-    // jump across code for "false"
-    if (both)
-      __ jmp(&loaded);
-    // reincarnate "false", if necessary
+
     if (false_target.is_linked()) {
       __ bind(&false_target);
       frame_->Push(Immediate(Factory::false_value()));
     }
-    // everything is loaded at this point
-    __ bind(&loaded);
   }
-  ASSERT(!has_cc());
 }