Fixed flooring division by a power of 2, once again...

Avoid right shifts by zero bits: On ARM it actually means shifting by
32 bits (correctness issue) and on other platforms they are useless
(performance issue). This is fix for the fix in r20544.

BUG=v8:3259
LOG=y
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/324403003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21769 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/lithium-codegen-arm.cc

@@ -1469,20 +1469,22 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
     DeoptimizeIf(eq, instr->environment());
   }
 
-  // If the negation could not overflow, simply shifting is OK.
-  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    __ mov(result, Operand(dividend, ASR, shift));
+  // Dividing by -1 is basically negation, unless we overflow.
+  if (divisor == -1) {
+    if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+      DeoptimizeIf(vs, instr->environment());
+    }
     return;
   }
 
-  // Dividing by -1 is basically negation, unless we overflow.
-  if (divisor == -1) {
-    DeoptimizeIf(vs, instr->environment());
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+    __ mov(result, Operand(result, ASR, shift));
     return;
   }
 
   __ mov(result, Operand(kMinInt / divisor), LeaveCC, vs);
-  __ mov(result, Operand(dividend, ASR, shift), LeaveCC, vc);
+  __ mov(result, Operand(result, ASR, shift), LeaveCC, vc);
 }
 
 

src/arm64/lithium-codegen-arm64.cc

@@ -3933,19 +3933,21 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
     DeoptimizeIf(eq, instr->environment());
   }
 
-  // If the negation could not overflow, simply shifting is OK.
-  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    __ Mov(result, Operand(dividend, ASR, shift));
+  // Dividing by -1 is basically negation, unless we overflow.
+  if (divisor == -1) {
+    if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+      DeoptimizeIf(vs, instr->environment());
+    }
     return;
   }
 
-  // Dividing by -1 is basically negation, unless we overflow.
-  if (divisor == -1) {
-    DeoptimizeIf(vs, instr->environment());
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+    __ Mov(result, Operand(dividend, ASR, shift));
     return;
   }
 
-  __ Asr(result, dividend, shift);
+  __ Asr(result, result, shift);
   __ Csel(result, result, kMinInt / divisor, vc);
 }
 

src/ia32/lithium-codegen-ia32.cc

@@ -1353,14 +1353,17 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
     DeoptimizeIf(zero, instr->environment());
   }
 
-  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    __ sar(dividend, shift);
+  // Dividing by -1 is basically negation, unless we overflow.
+  if (divisor == -1) {
+    if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+      DeoptimizeIf(overflow, instr->environment());
+    }
     return;
   }
 
-  // Dividing by -1 is basically negation, unless we overflow.
-  if (divisor == -1) {
-    DeoptimizeIf(overflow, instr->environment());
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+    __ sar(dividend, shift);
     return;
   }
 

src/x64/lithium-codegen-x64.cc

@@ -1134,16 +1134,17 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
     DeoptimizeIf(zero, instr->environment());
   }
 
-  // If the negation could not overflow, simply shifting is OK.
-  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    __ sarl(dividend, Immediate(shift));
+  // Dividing by -1 is basically negation, unless we overflow.
+  if (divisor == -1) {
+    if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+      DeoptimizeIf(overflow, instr->environment());
+    }
     return;
   }
 
-  // Note that we could emit branch-free code, but that would need one more
-  // register.
-  if (divisor == -1) {
-    DeoptimizeIf(overflow, instr->environment());
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+    __ sarl(dividend, Immediate(shift));
     return;
   }
 

test/mjsunit/mjsunit.status

@@ -308,10 +308,6 @@
   # Currently always deopt on minus zero
   'math-floor-of-div-minus-zero': [SKIP],
 
-  # Issue 3259.
-  'math-floor-of-div-nosudiv': [PASS, FAIL],
-  'math-floor-of-div': [PASS, FAIL],
-
   ############################################################################
   # Slow tests.
   'regress/regress-2185-2': [PASS, SLOW],