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8371534: C2: Missed Ideal optimization opportunity with AndL and URShiftL #28218

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8371534: C2: Missed Ideal optimization opportunity with AndL and URShiftL #28218

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eeddf77
Update test and add testURShiftL case
benoitmaillard Nov 10, 2025
8ba3fb3
Add missing case in add_users_of_use_to_worklist
benoitmaillard Nov 10, 2025
a518434
Format
benoitmaillard Nov 10, 2025
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5 changes: 3 additions & 2 deletions src/hotspot/share/opto/phaseX.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2550,11 +2550,12 @@ void PhaseIterGVN::add_users_of_use_to_worklist(Node* n, Node* use, Unique_Node_
}
}
}
// If changed AndI/AndL inputs, check RShift users for "(x & mask) >> shift" optimization opportunity
// If changed AndI/AndL inputs, check RShift/URShift users for "(x & mask) >> shift" optimization opportunity
if (use_op == Op_AndI || use_op == Op_AndL) {
for (DUIterator_Fast i2max, i2 = use->fast_outs(i2max); i2 < i2max; i2++) {
Node* u = use->fast_out(i2);
if (u->Opcode() == Op_RShiftI || u->Opcode() == Op_RShiftL) {
if (u->Opcode() == Op_RShiftI || u->Opcode() == Op_RShiftL ||
u->Opcode() == Op_URShiftI || u->Opcode() == Op_URShiftL) {
worklist.push(u);
}
}
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37 changes: 31 additions & 6 deletions test/hotspot/jtreg/compiler/c2/TestMaskAndRShiftReorder.java
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Expand Up @@ -23,12 +23,12 @@

/*
* @test
* @bug 8361700
* @bug 8361700 8371534
* @summary An expression of the form "(x & mask) >> shift", where the mask
* is a constant, should be transformed to "(x >> shift) & (mask >> shift)"
* VerifyIterativeGVN checks that this optimization was applied
* @run main/othervm -Xcomp -XX:+IgnoreUnrecognizedVMOptions
* -XX:CompileCommand=compileonly,compiler.c2.TestMaskAndRShiftReorder::test
* -XX:CompileCommand=compileonly,compiler.c2.TestMaskAndRShiftReorder::test*
* -XX:VerifyIterativeGVN=1110 compiler.c2.TestMaskAndRShiftReorder
* @run main compiler.c2.TestMaskAndRShiftReorder
*
Expand All @@ -41,20 +41,45 @@ public class TestMaskAndRShiftReorder {


public static void main(String[] strArr) {
test();
// No known reproducer with URShiftI so far
testRShiftI();
testRShiftL();
testURShiftL();
}

static long test() {
static void testRShiftI() {
int x = 10;
int y = -17;
int iArr[] = new int[10];
for (int i = 1; i < 7; i++) {
for (int j = 1; j < 2; j++) {
x <<= lFld;
}
y &= x;
y >>= 1;
}
return iArr.length;
}

static void testRShiftL() {
long x = 10;
long y = -17L;
for (int i = 1; i < 7; i++) {
for (int j = 1; j < 2; j++) {
x <<= lFld;
}
y &= x;
y >>= 1;
}
}

static void testURShiftL() {
long x = 10;
long y = -17L;
for (int i = 1; i < 7; i++) {
for (int j = 1; j < 2; j++) {
x <<= lFld;
}
y &= x;
y >>>= 1;
}
}
}