Optimize (x&A)<<B>>B.

Add an optimization to simplifyExpressionsPre to replace (x&A)<<B>>B with X&A
if possible. This comes up frequently in C++ with bool variables.

1 files changed, 17 insertions, 3 deletions

diff --git a/tools/test-js-optimizer-asm-pre-output.js b/tools/test-js-optimizer-asm-pre-output.js
index 72608aa8..ab953e5d 100644
--- a/tools/test-js-optimizer-asm-pre-output.js
+++ b/tools/test-js-optimizer-asm-pre-output.js
@@ -18,7 +18,7 @@ function b($this, $__n) {
   }
   $4 = $this;
   $5 = HEAP8[$4 & 16777215] | 0;
-  if (($5 & 1) << 24 >> 24 == 0) {
+  if (($5 & 1) == 0) {
     $14 = 10;
     $13 = $5;
   } else {
@@ -38,14 +38,14 @@ function b($this, $__n) {
   } else {
     $30 = $13;
   }
-  if (($30 & 1) << 24 >> 24 == 0) {
+  if (($30 & 1) == 0) {
     $38 = $this + 1 | 0;
   } else {
     $38 = HEAP32[($this + 8 & 16777215) >> 2] | 0;
   }
   _memset($38 + $23 | 0, 0, $__n | 0, 1, 1213141516);
   $40 = $23 + $__n | 0;
-  if ((HEAP8[$4 & 16777215] & 1) << 24 >> 24 == 0) {
+  if ((HEAP8[$4 & 16777215] & 1) == 0) {
     HEAP8[$4 & 16777215] = $40 << 1 & 255;
   } else {
     HEAP32[($this + 4 & 16777215) >> 2] = $40;
@@ -93,4 +93,18 @@ function i32_8() {
     print(5);
   }
 }
+function sign_extension_simplification() {
+  if ((HEAP8[$4 & 16777215] & 127) == 0) {
+    print(5);
+  }
+  if ((HEAP8[$4 & 16777215] & 128) << 24 >> 24 == 0) {
+    print(5);
+  }
+  if ((HEAP32[$5 & 16777215] & 32767) == 0) {
+    print(5);
+  }
+  if ((HEAP32[$5 & 16777215] & 32768) << 16 >> 16 == 0) {
+    print(5);
+  }
+}