Fixed flooring division by -1 on ARM.

We should avoid ASR #0 on ARM. Simplified and improved code a bit
while we're there on all platforms. Human brains are very bad at
understanding nested structures...

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

Review URL: https://codereview.chromium.org/227553003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20544 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 47b3a10..a19f3ae 100644 (file)
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -1469,19 +1469,21 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     DeoptimizeIf(eq, instr->environment());
   }
-  if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    // Note that we could emit branch-free code, but that would need one more
-    // register.
-    if (divisor == -1) {
-      DeoptimizeIf(vs, instr->environment());
-      __ mov(result, Operand(dividend, ASR, shift));
-    } else {
-      __ mov(result, Operand(kMinInt / divisor), LeaveCC, vs);
-      __ mov(result, Operand(dividend, ASR, shift), LeaveCC, vc);
-    }
-  } else {
+
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
     __ mov(result, Operand(dividend, ASR, shift));
+    return;
   }
+
+  // Dividing by -1 is basically negation, unless we overflow.
+  if (divisor == -1) {
+    DeoptimizeIf(vs, instr->environment());
+    return;
+  }
+
+  __ mov(result, Operand(kMinInt / divisor), LeaveCC, vs);
+  __ mov(result, Operand(dividend, ASR, shift), LeaveCC, vc);
 }
 
 

diff --git a/src/arm64/lithium-codegen-arm64.cc b/src/arm64/lithium-codegen-arm64.cc
index e52cc86..d885edd 100644 (file)
--- a/src/arm64/lithium-codegen-arm64.cc
+++ b/src/arm64/lithium-codegen-arm64.cc
@@ -3851,22 +3851,28 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
   }
 
   // If the divisor is negative, we have to negate and handle edge cases.
-  Label not_kmin_int, done;
   __ Negs(result, dividend);
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     DeoptimizeIf(eq, instr->environment());
   }
-  if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    // Note that we could emit branch-free code, but that would need one more
-    // register.
-    if (divisor == -1) {
-      DeoptimizeIf(vs, instr->environment());
-    } else {
-      __ B(vc, &not_kmin_int);
-      __ Mov(result, kMinInt / divisor);
-      __ B(&done);
-    }
+
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+    __ Mov(result, Operand(dividend, ASR, shift));
+    return;
   }
+
+  // Dividing by -1 is basically negation, unless we overflow.
+  if (divisor == -1) {
+    DeoptimizeIf(vs, instr->environment());
+    return;
+  }
+
+  // Using a conditional data processing instruction would need 1 more register.
+  Label not_kmin_int, done;
+  __ B(vc, &not_kmin_int);
+  __ Mov(result, kMinInt / divisor);
+  __ B(&done);
   __ bind(&not_kmin_int);
   __ Mov(result, Operand(dividend, ASR, shift));
   __ bind(&done);

diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 512cee4..66c4a5c 100644 (file)
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -1622,22 +1622,26 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
   }
 
   // If the divisor is negative, we have to negate and handle edge cases.
-  Label not_kmin_int, done;
   __ neg(dividend);
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     DeoptimizeIf(zero, instr->environment());
   }
-  if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    // Note that we could emit branch-free code, but that would need one more
-    // register.
-    if (divisor == -1) {
-      DeoptimizeIf(overflow, instr->environment());
-    } else {
-      __ j(no_overflow, &not_kmin_int, Label::kNear);
-      __ mov(dividend, Immediate(kMinInt / divisor));
-      __ jmp(&done, Label::kNear);
-    }
+
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+    __ sar(dividend, shift);
+    return;
   }
+
+  // Dividing by -1 is basically negation, unless we overflow.
+  if (divisor == -1) {
+    DeoptimizeIf(overflow, instr->environment());
+    return;
+  }
+
+  Label not_kmin_int, done;
+  __ j(no_overflow, &not_kmin_int, Label::kNear);
+  __ mov(dividend, Immediate(kMinInt / divisor));
+  __ jmp(&done, Label::kNear);
   __ bind(&not_kmin_int);
   __ sar(dividend, shift);
   __ bind(&done);

diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index a8536a1..a28d6c6 100644 (file)
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1139,22 +1139,28 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
   }
 
   // If the divisor is negative, we have to negate and handle edge cases.
-  Label not_kmin_int, done;
   __ negl(dividend);
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     DeoptimizeIf(zero, instr->environment());
   }
-  if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    // Note that we could emit branch-free code, but that would need one more
-    // register.
-    __ j(no_overflow, &not_kmin_int, Label::kNear);
-    if (divisor == -1) {
-      DeoptimizeIf(no_condition, instr->environment());
-    } else {
-      __ movl(dividend, Immediate(kMinInt / divisor));
-      __ jmp(&done, Label::kNear);
-    }
+
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+    __ sarl(dividend, Immediate(shift));
+    return;
   }
+
+  // Note that we could emit branch-free code, but that would need one more
+  // register.
+  if (divisor == -1) {
+    DeoptimizeIf(overflow, instr->environment());
+    return;
+  }
+
+  Label not_kmin_int, done;
+  __ j(no_overflow, &not_kmin_int, Label::kNear);
+  __ movl(dividend, Immediate(kMinInt / divisor));
+  __ jmp(&done, Label::kNear);
   __ bind(&not_kmin_int);
   __ sarl(dividend, Immediate(shift));
   __ bind(&done);