From 18c97e9b559c32be4e27a7156f4d7643d8716a15 Mon Sep 17 00:00:00 2001
From: Nia <niaow1234@gmail.com>
Date: Sat, 16 Jan 2021 14:27:35 -0500
Subject: [PATCH] Revert "compiler: saturate float-to-int conversions"

This reverts commit a867b56e5f9e6778f48a33d75b6543b0ca92dcc1.
---
 compiler/compiler.go | 65 ++------------------------------------------
 testdata/float.go    |  7 +----
 testdata/float.txt   |  2 +-
 3 files changed, 4 insertions(+), 70 deletions(-)

diff --git a/compiler/compiler.go b/compiler/compiler.go
index 35d42eef1..c5b7be658 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -8,7 +8,6 @@ import (
 	"go/constant"
 	"go/token"
 	"go/types"
-	"math/bits"
 	"path/filepath"
 	"sort"
 	"strconv"
@@ -2553,70 +2552,10 @@ func (b *builder) createConvert(typeFrom, typeTo types.Type, value llvm.Value, p
 
 		if typeFrom.Info()&types.IsFloat != 0 && typeTo.Info()&types.IsInteger != 0 {
 			// Conversion from float to int.
-			// Passing an out-of-bounds float to LLVM would cause UB, so that UB is trapped by select instructions.
-			// The Go specification says that this should be implementation-defined behavior.
-			// This implements saturating behavior, except that NaN is mapped to the minimum value.
-			var significandBits int
-			switch typeFrom.Kind() {
-			case types.Float32:
-				significandBits = 23
-			case types.Float64:
-				significandBits = 52
-			}
 			if typeTo.Info()&types.IsUnsigned != 0 { // if unsigned
-				// Select the maximum value for this unsigned integer type.
-				max := ^(^uint64(0) << uint(llvmTypeTo.IntTypeWidth()))
-				maxFloat := float64(max)
-				if bits.Len64(max) > significandBits {
-					// Round the max down to fit within the significand.
-					maxFloat = float64(max & ^uint64(0) << uint(bits.Len64(max)-significandBits))
-				}
-
-				// Check if the value is in-bounds (0 <= value <= max).
-				positive := b.CreateFCmp(llvm.FloatOLE, llvm.ConstNull(llvmTypeFrom), value, "positive")
-				withinMax := b.CreateFCmp(llvm.FloatOLE, value, llvm.ConstFloat(llvmTypeFrom, maxFloat), "withinmax")
-				inBounds := b.CreateAnd(positive, withinMax, "inbounds")
-
-				// Assuming that the value is out-of-bounds, select a saturated value.
-				saturated := b.CreateSelect(positive,
-					llvm.ConstInt(llvmTypeTo, max, false), // value > max
-					llvm.ConstNull(llvmTypeTo),            // value < 0 (or NaN)
-					"saturated",
-				)
-
-				// Do a normal conversion.
-				normal := b.CreateFPToUI(value, llvmTypeTo, "normal")
-
-				return b.CreateSelect(inBounds, normal, saturated, ""), nil
+				return b.CreateFPToUI(value, llvmTypeTo, ""), nil
 			} else { // if signed
-				// Select the minimum value for this signed integer type.
-				min := uint64(1) << uint(llvmTypeTo.IntTypeWidth()-1)
-				minFloat := -float64(min)
-
-				// Select the maximum value for this signed integer type.
-				max := ^(^uint64(0) << uint(llvmTypeTo.IntTypeWidth()-1))
-				maxFloat := float64(max)
-				if bits.Len64(max) > significandBits {
-					// Round the max down to fit within the significand.
-					maxFloat = float64(max & ^uint64(0) << uint(bits.Len64(max)-significandBits))
-				}
-
-				// Check if the value is in-bounds (min <= value <= max).
-				aboveMin := b.CreateFCmp(llvm.FloatOLE, llvm.ConstFloat(llvmTypeFrom, minFloat), value, "abovemin")
-				belowMax := b.CreateFCmp(llvm.FloatOLE, value, llvm.ConstFloat(llvmTypeFrom, maxFloat), "belowmax")
-				inBounds := b.CreateAnd(aboveMin, belowMax, "inbounds")
-
-				// Assuming that the value is out-of-bounds, select a saturated value.
-				saturated := b.CreateSelect(aboveMin,
-					llvm.ConstInt(llvmTypeTo, max, false), // value > max
-					llvm.ConstInt(llvmTypeTo, min, false), // value < min (or NaN)
-					"saturated",
-				)
-
-				// Do a normal conversion.
-				normal := b.CreateFPToSI(value, llvmTypeTo, "normal")
-
-				return b.CreateSelect(inBounds, normal, saturated, ""), nil
+				return b.CreateFPToSI(value, llvmTypeTo, ""), nil
 			}
 		}
 
diff --git a/testdata/float.go b/testdata/float.go
index 6d2d1bca6..8c33cf11b 100644
--- a/testdata/float.go
+++ b/testdata/float.go
@@ -29,12 +29,7 @@ func main() {
 	var f2 float32 = 5.7
 	var f3 float32 = -2.3
 	var f4 float32 = -11.8
-	var f5 float32 = -1
-	var f6 float32 = 256
-	var f7 float32 = -129
-	var f8 float32 = 0
-	f8 /= 0
-	println(int32(f1), int32(f2), int32(f3), int32(f4), uint8(f5), uint8(f6), int8(f7), int8(f6), uint8(f8), int8(f8))
+	println(int32(f1), int32(f2), int32(f3), int32(f4))
 
 	// int -> float
 	var i1 int32 = 53
diff --git a/testdata/float.txt b/testdata/float.txt
index 12c48598c..dbc36fb8a 100644
--- a/testdata/float.txt
+++ b/testdata/float.txt
@@ -11,7 +11,7 @@
 +3.333333e-001
 +6.666667e-001
 +6.666667e-001
-3 5 -2 -11 0 255 -128 127 0 -128
+3 5 -2 -11
 +5.300000e+001 -8.000000e+000 +2.000000e+001
 (+6.666667e-001+1.200000e+000i)
 +6.666667e-001