ARM: Do not set FPSCR when converting to clamped uint8

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index 1633adc1331e203edbacf85a6419a81b02e13653..5bba07ff05bb4ccb16926790b8b87f06a1d641aa 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -796,6 +796,14 @@ void MacroAssembler::VFPEnsureFPSCRState(Register scratch) {
   // If needed, restore wanted bits of FPSCR.
   Label fpscr_done;
   vmrs(scratch);
+  if (emit_debug_code()) {
+    Label rounding_mode_correct;
+    tst(scratch, Operand(kVFPRoundingModeMask));
+    b(eq, &rounding_mode_correct);
+    // Can't call Assert here, as it will recurse back here.
+    stop("Default rounding mode not set");
+    bind(&rounding_mode_correct);
+  }
   tst(scratch, Operand(kVFPDefaultNaNModeControlBit));
   b(ne, &fpscr_done);
   orr(scratch, scratch, Operand(kVFPDefaultNaNModeControlBit));
@@ -3800,36 +3808,19 @@ void MacroAssembler::ClampUint8(Register output_reg, Register input_reg) {
 void MacroAssembler::ClampDoubleToUint8(Register result_reg,
                                         DwVfpRegister input_reg,
                                         LowDwVfpRegister double_scratch) {
-  Label above_zero;
   Label done;
-  Label in_bounds;
-
-  VFPCompareAndSetFlags(input_reg, 0.0);
-  b(gt, &above_zero);
-
-  // Double value is less than zero, NaN or Inf, return 0.
-  mov(result_reg, Operand::Zero());
-  b(al, &done);
 
-  // Double value is >= 255, return 255.
-  bind(&above_zero);
+  // Handle inputs >= 255 (including +infinity).
   Vmov(double_scratch, 255.0, result_reg);
-  VFPCompareAndSetFlags(input_reg, double_scratch);
-  b(le, &in_bounds);
   mov(result_reg, Operand(255));
-  b(al, &done);
-
-  // In 0-255 range, round and truncate.
-  bind(&in_bounds);
-  // Save FPSCR.
-  vmrs(ip);
-  // Set rounding mode to round to the nearest integer by clearing bits[23:22].
-  bic(result_reg, ip, Operand(kVFPRoundingModeMask));
-  vmsr(result_reg);
-  vcvt_s32_f64(double_scratch.low(), input_reg, kFPSCRRounding);
+  VFPCompareAndSetFlags(input_reg, double_scratch);
+  b(ge, &done);
+
+  // For inputs < 255 (including negative) vcvt_u32_f64 with round-to-nearest
+  // rounding mode will provide the correct result.
+  vcvt_u32_f64(double_scratch.low(), input_reg, kFPSCRRounding);
   vmov(result_reg, double_scratch.low());
-  // Restore FPSCR.
-  vmsr(ip);
+
   bind(&done);
 }