Bug 1435756 - Clarify fallthrough in generated code for wasm truncate. r=bbouvier

--HG--
extra : source : ce16751adf656bb414257c3ab0450fcfb7f21ea9
extra : amend_source : 707316189f2e91d688117064e913ef18dc6d5ace

js/src/jit/x86-shared/MacroAssembler-x86-shared.cpp

@@ -683,7 +683,7 @@ struct MOZ_RAII AutoHandleWasmTruncateToIntErrors
 {
     MacroAssembler& masm;
     Label inputIsNaN;
-    Label fail;
+    Label intOverflow;
     wasm::BytecodeOffset off;
 
     explicit AutoHandleWasmTruncateToIntErrors(MacroAssembler& masm, wasm::BytecodeOffset off)
@@ -691,8 +691,9 @@ struct MOZ_RAII AutoHandleWasmTruncateToIntErrors
     { }
 
     ~AutoHandleWasmTruncateToIntErrors() {
-        // Handle errors.
-        masm.bind(&fail);
+        // Handle errors.  These cases are not in arbitrary order: code will
+        // fall through to intOverflow.
+        masm.bind(&intOverflow);
         masm.jump(wasm::OldTrapDesc(off, wasm::Trap::IntegerOverflow, masm.framePushed()));
 
         masm.bind(&inputIsNaN);
@@ -725,17 +726,19 @@ MacroAssembler::oolWasmTruncateCheckF64ToI32(FloatRegister input, bool isUnsigne
     // Eagerly take care of NaNs.
     branchDouble(Assembler::DoubleUnordered, input, input, &traps.inputIsNaN);
 
-    // Handle special values (not needed for unsigned values).
+    // For unsigned, fall through to intOverflow failure case.
     if (isUnsigned)
         return;
 
+    // Handle special values.
+
     // We've used vcvttsd2si. The only valid double values that can
     // truncate to INT32_MIN are in ]INT32_MIN - 1; INT32_MIN].
     loadConstantDouble(double(INT32_MIN) - 1.0, ScratchDoubleReg);
-    branchDouble(Assembler::DoubleLessThanOrEqual, input, ScratchDoubleReg, &traps.fail);
+    branchDouble(Assembler::DoubleLessThanOrEqual, input, ScratchDoubleReg, &traps.intOverflow);
 
     loadConstantDouble(double(INT32_MIN), ScratchDoubleReg);
-    branchDouble(Assembler::DoubleGreaterThan, input, ScratchDoubleReg, &traps.fail);
+    branchDouble(Assembler::DoubleGreaterThan, input, ScratchDoubleReg, &traps.intOverflow);
     jump(rejoin);
 }
 
@@ -748,15 +751,17 @@ MacroAssembler::oolWasmTruncateCheckF32ToI32(FloatRegister input, bool isUnsigne
     // Eagerly take care of NaNs.
     branchFloat(Assembler::DoubleUnordered, input, input, &traps.inputIsNaN);
 
-    // Handle special values (not needed for unsigned values).
+    // For unsigned, fall through to intOverflow failure case.
     if (isUnsigned)
         return;
 
+    // Handle special values.
+
     // We've used vcvttss2si. Check that the input wasn't
     // float(INT32_MIN), which is the only legimitate input that
     // would truncate to INT32_MIN.
     loadConstantFloat32(float(INT32_MIN), ScratchFloat32Reg);
-    branchFloat(Assembler::DoubleNotEqual, input, ScratchFloat32Reg, &traps.fail);
+    branchFloat(Assembler::DoubleNotEqual, input, ScratchFloat32Reg, &traps.intOverflow);
     jump(rejoin);
 }
 
@@ -772,9 +777,9 @@ MacroAssembler::oolWasmTruncateCheckF64ToI64(FloatRegister input, bool isUnsigne
     // Handle special values.
     if (isUnsigned) {
         loadConstantDouble(-0.0, ScratchDoubleReg);
-        branchDouble(Assembler::DoubleGreaterThan, input, ScratchDoubleReg, &traps.fail);
+        branchDouble(Assembler::DoubleGreaterThan, input, ScratchDoubleReg, &traps.intOverflow);
         loadConstantDouble(-1.0, ScratchDoubleReg);
-        branchDouble(Assembler::DoubleLessThanOrEqual, input, ScratchDoubleReg, &traps.fail);
+        branchDouble(Assembler::DoubleLessThanOrEqual, input, ScratchDoubleReg, &traps.intOverflow);
         jump(rejoin);
         return;
     }
@@ -783,7 +788,7 @@ MacroAssembler::oolWasmTruncateCheckF64ToI64(FloatRegister input, bool isUnsigne
     // truncation is INT64_MIN is double(INT64_MIN): exponent is so
     // high that the highest resolution around is much more than 1.
     loadConstantDouble(double(int64_t(INT64_MIN)), ScratchDoubleReg);
-    branchDouble(Assembler::DoubleNotEqual, input, ScratchDoubleReg, &traps.fail);
+    branchDouble(Assembler::DoubleNotEqual, input, ScratchDoubleReg, &traps.intOverflow);
     jump(rejoin);
 }
 
@@ -799,16 +804,16 @@ MacroAssembler::oolWasmTruncateCheckF32ToI64(FloatRegister input, bool isUnsigne
     // Handle special values.
     if (isUnsigned) {
         loadConstantFloat32(-0.0f, ScratchFloat32Reg);
-        branchFloat(Assembler::DoubleGreaterThan, input, ScratchFloat32Reg, &traps.fail);
+        branchFloat(Assembler::DoubleGreaterThan, input, ScratchFloat32Reg, &traps.intOverflow);
         loadConstantFloat32(-1.0f, ScratchFloat32Reg);
-        branchFloat(Assembler::DoubleLessThanOrEqual, input, ScratchFloat32Reg, &traps.fail);
+        branchFloat(Assembler::DoubleLessThanOrEqual, input, ScratchFloat32Reg, &traps.intOverflow);
         jump(rejoin);
         return;
     }
 
     // We've used vcvtss2sq. See comment in outOfLineWasmTruncateDoubleToInt64.
     loadConstantFloat32(float(int64_t(INT64_MIN)), ScratchFloat32Reg);
-    branchFloat(Assembler::DoubleNotEqual, input, ScratchFloat32Reg, &traps.fail);
+    branchFloat(Assembler::DoubleNotEqual, input, ScratchFloat32Reg, &traps.intOverflow);
     jump(rejoin);
 }