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During SSA construction do a liveness check prior to inserting a phi #40

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Merged
dibyendumajumdar merged 2 commits into main from develop
Mar 30, 2025
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,7 @@ public Map<Integer, Integer> assignRegisters(CompiledFunction function, int numR
* Frame size = max number of registers needed to execute the function
*/
private int computeFrameSize(Map<Integer, Integer> assignments) {
return assignments.values().stream().mapToInt(k->k).max().orElse(0);
return assignments.values().stream().mapToInt(k->k).max().orElse(-1)+1;
}

/**
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ public class CompiledFunction {
public BasicBlock currentBlock;
private BasicBlock currentBreakTarget;
private BasicBlock currentContinueTarget;
private Type.TypeFunction functionType;
public Type.TypeFunction functionType;
public final RegisterPool registerPool;
private final TypeDictionary typeDictionary;

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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,7 @@ public EnterSSA(CompiledFunction bytecodeFunction, EnumSet<Options> options) {
}
this.blocks = domTree.blocks; // the blocks are ordered reverse post order
findNonLocalNames();
new Liveness(bytecodeFunction); // EWe require liveness info to construct pruned ssa
insertPhis();
renameVars();
bytecodeFunction.isSSA = true;
Expand Down Expand Up @@ -94,12 +95,16 @@ void insertPhis() {
while (b != null) {
visited.set(b.bid);
for (BasicBlock d: b.dominationFrontier) {
if (d == function.exit) // The exit block does not need any phis as it has no instructions
continue;
// insert phi for x in d
d.insertPhiFor(x);
if (!visited.get(d.bid))
worklist.push(d);
// Perform a liveness check to avoid inserting
// phi when variable is dead
// Inserting dead phis causes problems during renaming
// because there will not be a definition available
if (d.liveIn.contains(x)) {
// insert phi for x in d
d.insertPhiFor(x);
if (!visited.get(d.bid))
worklist.push(d);
}
}
b = worklist.pop();
}
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Original file line number Diff line number Diff line change
Expand Up @@ -520,5 +520,154 @@ func foo(x: Int,y: Int)->Int
""", result);
}

@Test
public void testSSA10() {
String src = """
func main()->Int {
var sum = 0
var i = 0
var j = 0
while (i < 5) {
j = 0
while (j < 5) {
if (j % 2 == 0)
sum = sum + j
j = j + 1
}
i = i + 1
}
return sum
}
""";
String result = compileSrc(src);
Assert.assertEquals("""
func main()->Int
Reg #0 sum 0
Reg #1 i 1
Reg #2 j 2
Reg #3 %t3 3
Reg #4 i_1 1
Reg #5 j_1 2
Reg #6 %t6 6
Reg #7 j_2 2
Reg #8 %t8 8
Reg #9 %t9 9
Reg #10 %t10 10
Reg #11 sum_1 0
Reg #12 sum_2 0
Reg #13 %t13 13
Reg #14 j_3 2
Reg #15 j_4 2
Reg #16 sum_3 0
Reg #17 sum_4 0
Reg #18 %t18 18
Reg #19 i_2 1
Reg #20 i_3 1
Reg #21 i_4 1
L0:
sum = 0
i = 0
j = 0
goto L2
L2:
sum_3 = phi(sum, sum_1)
i_1 = phi(i, i_4)
%t3 = i_1<5
if %t3 goto L3 else goto L4
L3:
j_1 = 0
goto L5
L5:
sum_1 = phi(sum_3, sum_4)
j_2 = phi(j_1, j_4)
%t6 = j_2<5
if %t6 goto L6 else goto L7
L6:
%t8 = j_2%2
%t9 = %t8==0
if %t9 goto L8 else goto L9
L8:
%t10 = sum_1+j_2
sum_2 = %t10
goto L9
L9:
sum_4 = phi(sum_1, sum_2)
%t13 = j_2+1
j_4 = %t13
goto L5
L7:
%t18 = i_1+1
i_4 = %t18
goto L2
L4:
ret sum_3
goto L1
L1:
""", result);
}

@Test
public void testSSA17() {
String src = """
func merge(begin: Int, middle: Int, end: Int)
{
if (begin < end) {
var cond = 0
if (begin < middle) {
if (begin >= end) cond = 1;
}
if (cond)
{
cond = 0
}
}
}
""";
String result = compileSrc(src);
Assert.assertEquals("""
func merge(begin: Int,middle: Int,end: Int)
Reg #0 begin 0
Reg #1 middle 1
Reg #2 end 2
Reg #3 cond 3
Reg #4 %t4 4
Reg #5 %t5 5
Reg #6 %t6 6
Reg #7 cond_1 3
Reg #8 cond_2 3
Reg #9 cond_3 3
Reg #10 cond_4 3
L0:
arg begin
arg middle
arg end
%t4 = begin<end
if %t4 goto L2 else goto L3
L2:
cond = 0
%t5 = begin<middle
if %t5 goto L4 else goto L5
L4:
%t6 = begin>=end
if %t6 goto L6 else goto L7
L6:
cond_1 = 1
goto L7
L7:
cond_3 = phi(cond, cond_1)
goto L5
L5:
cond_2 = phi(cond, cond_3)
if cond_2 goto L8 else goto L9
L8:
cond_4 = 0
goto L9
L9:
goto L3
L3:
goto L1
L1:
""", result);
}

}
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