Chromium Code Reviews
chromiumcodereview-hr@appspot.gserviceaccount.com (chromiumcodereview-hr) | Please choose your nickname with Settings | Help | Chromium Project | Gerrit Changes | Sign out
(37)

Unified Diff: src/arm/lithium-arm.cc

Issue 10197010: Optimise Math.floor(x/y) to use integer division for specific divisor. (Closed) Base URL: http://v8.googlecode.com/svn/branches/bleeding_edge/
Patch Set: Created 8 years, 8 months ago
Use n/p to move between diff chunks; N/P to move between comments. Draft comments are only viewable by you.
Jump to:
View side-by-side diff with in-line comments
Download patch
« no previous file with comments | « src/arm/lithium-arm.h ('k') | src/arm/lithium-codegen-arm.h » ('j') | no next file with comments »
Expand Comments ('e') | Collapse Comments ('c') | Show Comments Hide Comments ('s')
Index: src/arm/lithium-arm.cc
===================================================================
--- src/arm/lithium-arm.cc (revision 11426)
+++ src/arm/lithium-arm.cc (working copy)
@@ -1315,6 +1315,75 @@
}
+bool LChunkBuilder::HasMagicNumberForDivisor(int32_t divisor) {
+ uint32_t divisor_abs = abs(divisor);
+ // Dividing by 0, 1, and powers of 2 is easy.
+ // Note that IsPowerOf2(0) returns true;
+ ASSERT(IsPowerOf2(0) == true);
+ if (IsPowerOf2(divisor_abs)) return true;
+
+ // We have magic numbers for a few specific divisors.
+ // Details and proofs can be found in:
+ // - Hacker's Delight, Henry S. Warren, Jr.
+ // - The PowerPC Compiler Writer’s Guide
+ // and probably many others.
+ //
+ // We handle
+ // <divisor with magic numbers> * <power of 2>
+ // but not
+ // <divisor with magic numbers> * <other divisor with magic numbers>
+ int32_t power_of_2_factor =
+ CompilerIntrinsics::CountTrailingZeros(divisor_abs);
+ DivMagicNumbers magic_numbers =
+ DivMagicNumberFor(divisor_abs >> power_of_2_factor);
+ if (magic_numbers.M != InvalidDivMagicNumber.M) return true;
+
+ return false;
+}
+
+
+HValue* LChunkBuilder::SimplifiedDividendForMathFloorOfDiv(HValue* dividend) {
+ // A value with an integer representation does not need to be transformed.
+ if (dividend->representation().IsInteger32()) {
+ return dividend;
+ // A change from an integer32 can be replaced by the integer32 value.
+ } else if (dividend->IsChange() &&
+ HChange::cast(dividend)->from().IsInteger32()) {
+ return HChange::cast(dividend)->value();
+ }
+ return NULL;
+}
+
+
+HValue* LChunkBuilder::SimplifiedDivisorForMathFloorOfDiv(HValue* divisor) {
+ // Only optimize when we have magic numbers for the divisor.
+ // The standard integer division routine is usually slower than transitionning
+ // to VFP.
+ if (divisor->IsConstant() &&
+ HConstant::cast(divisor)->HasInteger32Value()) {
+ HConstant* constant_val = HConstant::cast(divisor);
+ int32_t int32_val = constant_val->Integer32Value();
+ if (LChunkBuilder::HasMagicNumberForDivisor(int32_val)) {
+ return constant_val->CopyToRepresentation(Representation::Integer32());
+ }
+ }
+ return NULL;
+}
+
+
+LInstruction* LChunkBuilder::DoMathFloorOfDiv(HMathFloorOfDiv* instr) {
+ HValue* right = instr->right();
+ LOperand* dividend = UseRegister(instr->left());
+ LOperand* divisor = UseRegisterOrConstant(right);
+ LOperand* remainder = TempRegister();
+ ASSERT(right->IsConstant() &&
+ HConstant::cast(right)->HasInteger32Value() &&
+ HasMagicNumberForDivisor(HConstant::cast(right)->Integer32Value()));
+ return AssignEnvironment(DefineAsRegister(
+ new LMathFloorOfDiv(dividend, divisor, remainder)));
+}
+
+
LInstruction* LChunkBuilder::DoMod(HMod* instr) {
if (instr->representation().IsInteger32()) {
ASSERT(instr->left()->representation().IsInteger32());
« no previous file with comments | « src/arm/lithium-arm.h ('k') | src/arm/lithium-codegen-arm.h » ('j') | no next file with comments »

Powered by Google App Engine
This is Rietveld 408576698