Remove UB from int-to-float conversion for INT_MIN.

Author: pnkfelix

lib/builtins/floatsidf.c

@@ -21,30 +21,32 @@
 ARM_EABI_FNALIAS(i2d, floatsidf)
 
 COMPILER_RT_ABI fp_t
-__floatsidf(int a) {
+__floatsidf(int a_orig) {
 
-    const int aWidth = sizeof a * CHAR_BIT;
+    const int aWidth = sizeof a_orig * CHAR_BIT;
+
+    // unsigned int representation is necessary to avoid
+    // undefined behavior for the input INT_MIN.
+    unsigned int a = (unsigned int) a_orig;
 
     // Handle zero as a special case to protect clz
     if (a == 0)
         return fromRep(0);
 
     // All other cases begin by extracting the sign and absolute value of a
     rep_t sign = 0;
-    if (a < 0) {
+    if (a_orig < 0) {
         sign = signBit;
-        a = -a;
+        a = ~a + 1; // same as (unsigned int)-a_orig, but defined for INT_MIN
     }
 
     // Exponent of (fp_t)a is the width of abs(a).
     const int exponent = (aWidth - 1) - __builtin_clz(a);
     rep_t result;
 
-    // Shift a into the significand field and clear the implicit bit.  Extra
-    // cast to unsigned int is necessary to get the correct behavior for
-    // the input INT_MIN.
+    // Shift a into the significand field and clear the implicit bit.
     const int shift = significandBits - exponent;
-    result = (rep_t)(unsigned int)a << shift ^ implicitBit;
+    result = (rep_t)a << shift ^ implicitBit;
 
     // Insert the exponent
     result += (rep_t)(exponent + exponentBias) << significandBits;

lib/builtins/floatsisf.c

@@ -21,19 +21,23 @@
 ARM_EABI_FNALIAS(i2f, floatsisf)
 
 COMPILER_RT_ABI fp_t
-__floatsisf(int a) {
+__floatsisf(int a_orig) {
 
     const int aWidth = sizeof a * CHAR_BIT;
+
+    // unsigned int representation is necessary to avoid
+    // undefined behavior for the input INT_MIN.
+    unsigned int a = (unsigned int) a_orig;
 
     // Handle zero as a special case to protect clz
     if (a == 0)
         return fromRep(0);
 
     // All other cases begin by extracting the sign and absolute value of a
     rep_t sign = 0;
-    if (a < 0) {
+    if (a_orig < 0) {
         sign = signBit;
-        a = -a;
+        a = ~a + 1; // same as (unsigned int)-a_orig, but defined for INT_MIN
     }
 
     // Exponent of (fp_t)a is the width of abs(a).