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Optimize branch instructions to short form at known-small-distance sites #529

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Merged
dadhi merged 5 commits into from
Apr 27, 2026
Merged

Optimize branch instructions to short form at known-small-distance sites #529

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9717001
Initial plan
Copilot Apr 22, 2026
99a07a2
Optimize branches to use short form where possible
Copilot Apr 22, 2026
b17f751
Fix label tracking to use Label struct directly instead of GetHashCode
Copilot Apr 22, 2026
4692876
Refactor: extract shared helper TryGetShortFormOpCodeForBackwardBranch
Copilot Apr 22, 2026
f4fc8ab
Drop ConditionalWeakTable general backward-branch optimizer, keep onl…
Copilot Apr 27, 2026
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12 changes: 6 additions & 6 deletions src/FastExpressionCompiler/FastExpressionCompiler.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2568,7 +2568,7 @@ private static bool TryEmitCoalesceOperator(BinaryExpression expr, ILGenerator i
il.DmarkLabel(labelFalse);
else
{
il.Demit(OpCodes.Br, labelDone);
il.Demit(OpCodes.Br_S, labelDone); // safe: jumps over Castclass (5 bytes) = 5 bytes
il.DmarkLabel(labelFalse); // todo: @bug? should we insert the boxing for the Nullable value type before the Castclass
il.Demit(OpCodes.Castclass, exprType);
il.DmarkLabel(labelDone);
Expand Down Expand Up @@ -2947,9 +2947,9 @@ private static bool TryEmitSimpleUnaryExpression(UnaryExpression expr, Expressio
{
var falseLabel = il.DefineLabel();
var continueLabel = il.DefineLabel();
il.Demit(OpCodes.Brfalse, falseLabel);
il.Demit(OpCodes.Brfalse_S, falseLabel); // safe: jumps over Ldc_I4_0 (1 byte) + Br_S (2 bytes) = 3 bytes
il.Demit(OpCodes.Ldc_I4_0);
il.Demit(OpCodes.Br, continueLabel);
il.Demit(OpCodes.Br_S, continueLabel); // safe: jumps over Ldc_I4_1 (1 byte) = 1 byte
il.DmarkLabel(falseLabel);
il.Demit(OpCodes.Ldc_I4_1);
il.DmarkLabel(continueLabel);
Expand Down Expand Up @@ -5767,9 +5767,9 @@ var methodName
var resultLabel = il.DefineLabel();
var isNullLabel = il.DefineLabel();
EmitLoadLocalVariable(il, leftHasValueVar);
il.Demit(OpCodes.Brfalse, isNullLabel);
il.Demit(OpCodes.Brfalse_S, isNullLabel); // safe: jumps over EmitLoadLocalVariable (1-4 bytes) + Brtrue_S (2 bytes) = 3-6 bytes
EmitLoadLocalVariable(il, rightHasValueVar);
il.Demit(OpCodes.Brtrue, resultLabel);
il.Demit(OpCodes.Brtrue_S, resultLabel); // safe: jumps over Pop (1 byte) + Ldnull (1 byte) = 2 bytes
il.DmarkLabel(isNullLabel);
il.Demit(OpCodes.Pop);
il.Demit(OpCodes.Ldnull);
Expand Down Expand Up @@ -5974,7 +5974,7 @@ private static bool TryEmitLogicalOperator(BinaryExpression expr, ExpressionType
return false;

var labelDone = il.DefineLabel();
il.Demit(OpCodes.Br, labelDone);
il.Demit(OpCodes.Br_S, labelDone); // safe: jumps over Ldc_I4_0 or Ldc_I4_1 (1 byte) = 1 byte

il.DmarkLabel(labelSkipRight); // label the second branch
il.Demit(nodeType == ExpressionType.AndAlso ? OpCodes.Ldc_I4_0 : OpCodes.Ldc_I4_1);
Expand Down
2 changes: 1 addition & 1 deletion test/FastExpressionCompiler.IssueTests/Issue159_NumericConversions.cs
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Expand Up @@ -365,7 +365,7 @@ public void ComparisonsWithConversionsShouldWork4()
OpCodes.Cgt_Un,
OpCodes.Ldc_I4_0,
OpCodes.Ceq,
OpCodes.Br,
OpCodes.Br_S, // short form: jumps over Ldc_I4_0 (1 byte) = 1 byte
OpCodes.Ldc_I4_0,
OpCodes.Ret);

Expand Down
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