diff --git a/src/codegen/expressions/access/index.ts b/src/codegen/expressions/access/index.ts
index 792ae3fc..d1113300 100644
--- a/src/codegen/expressions/access/index.ts
+++ b/src/codegen/expressions/access/index.ts
@@ -201,6 +201,9 @@ export class IndexAccessGenerator {
     this.ctx.emit(`call void @__cs_bounds_fail(i32 ${index}, i32 ${len})`);
     this.ctx.emit(`unreachable`);
     this.ctx.emit(`${okLabel}:`);
+    const inBounds = this.ctx.nextTemp();
+    this.ctx.emit(`${inBounds} = icmp ult i32 ${index}, ${len}`);
+    this.ctx.emit(`call void @llvm.assume(i1 ${inBounds})`);
   }
 
   private generateStringArrayIndex(expr: IndexAccessNode, params: string[]): string {
diff --git a/src/codegen/expressions/operators/binary.ts b/src/codegen/expressions/operators/binary.ts
index 860a612a..17dac293 100644
--- a/src/codegen/expressions/operators/binary.ts
+++ b/src/codegen/expressions/operators/binary.ts
@@ -88,12 +88,12 @@ export class BinaryExpressionGenerator {
     const leftValue = this.ctx.generateExpression(left, params);
     const rightValue = this.ctx.generateExpression(right, params);
 
-    // Arithmetic operators (floating-point)
+    // Arithmetic operators (floating-point) — fast-math flags enable LLVM optimizations
     const arithMap: { [key: string]: string } = {
-      "+": "fadd nsz arcp contract reassoc afn",
-      "-": "fsub nsz arcp contract reassoc afn",
-      "*": "fmul nsz arcp contract reassoc afn",
-      "/": "fdiv nsz arcp contract reassoc afn",
+      "+": "fadd nnan ninf nsz arcp contract reassoc afn",
+      "-": "fsub nnan ninf nsz arcp contract reassoc afn",
+      "*": "fmul nnan ninf nsz arcp contract reassoc afn",
+      "/": "fdiv nnan ninf nsz arcp contract reassoc afn",
     };
 
     // Bitwise operators (need to convert double -> i64 -> operate -> double)
diff --git a/src/codegen/infrastructure/ir-builders.ts b/src/codegen/infrastructure/ir-builders.ts
index 81eaef00..5f80b40f 100644
--- a/src/codegen/infrastructure/ir-builders.ts
+++ b/src/codegen/infrastructure/ir-builders.ts
@@ -25,30 +25,32 @@ export function emitMul(ctx: EmitContext, type: string, lhs: string, rhs: string
   return temp;
 }
 
+const FMATH = "nnan ninf nsz arcp contract reassoc afn";
+
 export function emitFAdd(ctx: EmitContext, lhs: string, rhs: string): string {
   const temp = ctx.nextTemp();
-  ctx.emit(`${temp} = fadd double ${lhs}, ${rhs}`);
+  ctx.emit(`${temp} = fadd ${FMATH} double ${lhs}, ${rhs}`);
   ctx.setVariableType(temp, "double");
   return temp;
 }
 
 export function emitFSub(ctx: EmitContext, lhs: string, rhs: string): string {
   const temp = ctx.nextTemp();
-  ctx.emit(`${temp} = fsub double ${lhs}, ${rhs}`);
+  ctx.emit(`${temp} = fsub ${FMATH} double ${lhs}, ${rhs}`);
   ctx.setVariableType(temp, "double");
   return temp;
 }
 
 export function emitFMul(ctx: EmitContext, lhs: string, rhs: string): string {
   const temp = ctx.nextTemp();
-  ctx.emit(`${temp} = fmul double ${lhs}, ${rhs}`);
+  ctx.emit(`${temp} = fmul ${FMATH} double ${lhs}, ${rhs}`);
   ctx.setVariableType(temp, "double");
   return temp;
 }
 
 export function emitFDiv(ctx: EmitContext, lhs: string, rhs: string): string {
   const temp = ctx.nextTemp();
-  ctx.emit(`${temp} = fdiv double ${lhs}, ${rhs}`);
+  ctx.emit(`${temp} = fdiv ${FMATH} double ${lhs}, ${rhs}`);
   ctx.setVariableType(temp, "double");
   return temp;
 }
@@ -62,14 +64,14 @@ export function emitSRem(ctx: EmitContext, type: string, lhs: string, rhs: strin
 
 export function emitFRem(ctx: EmitContext, lhs: string, rhs: string): string {
   const temp = ctx.nextTemp();
-  ctx.emit(`${temp} = frem double ${lhs}, ${rhs}`);
+  ctx.emit(`${temp} = frem ${FMATH} double ${lhs}, ${rhs}`);
   ctx.setVariableType(temp, "double");
   return temp;
 }
 
 export function emitFNeg(ctx: EmitContext, value: string): string {
   const temp = ctx.nextTemp();
-  ctx.emit(`${temp} = fneg double ${value}`);
+  ctx.emit(`${temp} = fneg ${FMATH} double ${value}`);
   ctx.setVariableType(temp, "double");
   return temp;
 }
diff --git a/src/codegen/infrastructure/llvm-declarations.ts b/src/codegen/infrastructure/llvm-declarations.ts
index 8a3935c3..8986b829 100644
--- a/src/codegen/infrastructure/llvm-declarations.ts
+++ b/src/codegen/infrastructure/llvm-declarations.ts
@@ -51,6 +51,7 @@ export function getLLVMDeclarations(config?: DeclConfig): string {
   ir += "declare i8* @strstr(i8*, i8*)\n";
   ir += "declare i8* @strchr(i8*, i32)\n";
   ir += "declare i8* @strrchr(i8*, i32)\n";
+  ir += "declare void @llvm.assume(i1)\n";
   ir += "declare void @llvm.memcpy.p0i8.p0i8.i64(i8*, i8*, i64, i1)\n";
   ir += "declare void @llvm.memmove.p0i8.p0i8.i64(i8*, i8*, i64, i1)\n";
   ir += "declare void @llvm.memset.p0i8.i64(i8*, i8, i64, i1)\n";