arch-arm: Fix some poorly done type max and min in NEON

The ISA code for ARM calculates min and max elements for types using
bit manipulation. That triggers some warnings, treated as errors, as
the compiler can tell that there is an overflow and the sign
flips. Fixed using standard lib definitions instead.

Change-Id: Ie2331b410c7f76d4bd87da5afe9edf20c8ac91b3
Reviewed-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/3481
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

1 files changed, 20 insertions, 16 deletions

diff --git a/src/arch/arm/isa/insts/neon.isa b/src/arch/arm/isa/insts/neon.isa
index 163b71c13..64419e46a 100644
--- a/src/arch/arm/isa/insts/neon.isa
+++ b/src/arch/arm/isa/insts/neon.isa
@@ -2170,9 +2170,12 @@ let {{
         bool negSrc1 = (srcElem1 < 0);
         bool negSrc2 = (srcElem2 < 0);
         if ((negDest != negSrc1) && (negSrc1 == negSrc2)) {
-            destElem = (Element)1 << (sizeof(Element) * 8 - 1);
             if (negDest)
-                destElem -= 1;
+                /* If (>=0) plus (>=0) yields (<0), saturate to +. */
+                destElem = std::numeric_limits<Element>::max();
+            else
+                /* If (<0) plus (<0) yields (>=0), saturate to -. */
+                destElem = std::numeric_limits<Element>::min();
             fpscr.qc = 1;
         }
         FpscrQc = fpscr;
@@ -2199,9 +2202,12 @@ let {{
         bool negSrc1 = (srcElem1 < 0);
         bool posSrc2 = (srcElem2 >= 0);
         if ((negDest != negSrc1) && (negSrc1 == posSrc2)) {
-            destElem = (Element)1 << (sizeof(Element) * 8 - 1);
             if (negDest)
-                destElem -= 1;
+                /* If (>=0) minus (<0) yields (<0), saturate to +. */
+                destElem = std::numeric_limits<Element>::max();
+            else
+                /* If (<0) minus (>=0) yields (>=0), saturate to -. */
+                destElem = std::numeric_limits<Element>::min();
             fpscr.qc = 1;
         }
         FpscrQc = fpscr;
@@ -2514,7 +2520,7 @@ let {{
     vqdmlalCode = '''
         FPSCR fpscr = (FPSCR) FpscrQc;
         BigElement midElem = (2 * (int64_t)srcElem1 * (int64_t)srcElem2);
-        Element maxNeg = (Element)1 << (sizeof(Element) * 8 - 1);
+        Element maxNeg = std::numeric_limits<Element>::min();
         Element halfNeg = maxNeg / 2;
         if ((srcElem1 == maxNeg && srcElem2 == maxNeg) ||
             (srcElem1 == halfNeg && srcElem2 == maxNeg) ||
@@ -2539,7 +2545,7 @@ let {{
     vqdmlslCode = '''
         FPSCR fpscr = (FPSCR) FpscrQc;
         BigElement midElem = (2 * (int64_t)srcElem1 * (int64_t)srcElem2);
-        Element maxNeg = (Element)1 << (sizeof(Element) * 8 - 1);
+        Element maxNeg = std::numeric_limits<Element>::min();
         Element halfNeg = maxNeg / 2;
         if ((srcElem1 == maxNeg && srcElem2 == maxNeg) ||
             (srcElem1 == halfNeg && srcElem2 == maxNeg) ||
@@ -2565,8 +2571,7 @@ let {{
         FPSCR fpscr = (FPSCR) FpscrQc;
         destElem = (2 * (int64_t)srcElem1 * (int64_t)srcElem2);
         if (srcElem1 == srcElem2 &&
-                srcElem1 == (Element)((Element)1 <<
-                    (Element)(sizeof(Element) * 8 - 1))) {
+                srcElem1 == (Element)(std::numeric_limits<Element>::min())) {
             destElem = ~((BigElement)srcElem1 << (sizeof(Element) * 8));
             fpscr.qc = 1;
         }
@@ -2611,8 +2616,7 @@ let {{
         destElem = (2 * (int64_t)srcElem1 * (int64_t)srcElem2) >>
                    (sizeof(Element) * 8);
         if (srcElem1 == srcElem2 &&
-                srcElem1 == (Element)((Element)1 <<
-                    (sizeof(Element) * 8 - 1))) {
+                srcElem1 == (Element)(std::numeric_limits<Element>::min())) {
             destElem = ~srcElem1;
             fpscr.qc = 1;
         }
@@ -2626,7 +2630,7 @@ let {{
         destElem = (2 * (int64_t)srcElem1 * (int64_t)srcElem2 +
                     ((int64_t)1 << (sizeof(Element) * 8 - 1))) >>
                    (sizeof(Element) * 8);
-        Element maxNeg = (Element)1 << (sizeof(Element) * 8 - 1);
+        Element maxNeg = std::numeric_limits<Element>::min();
         Element halfNeg = maxNeg / 2;
         if ((srcElem1 == maxNeg && srcElem2 == maxNeg) ||
             (srcElem1 == halfNeg && srcElem2 == maxNeg) ||
@@ -2634,7 +2638,7 @@ let {{
             if (destElem < 0) {
                 destElem = mask(sizeof(Element) * 8 - 1);
             } else {
-                destElem = (Element)1 << (sizeof(Element) * 8 - 1);
+                destElem = std::numeric_limits<Element>::min();
             }
             fpscr.qc = 1;
         }
@@ -2973,7 +2977,7 @@ let {{
         FPSCR fpscr = (FPSCR) FpscrQc;
         if (imm >= sizeof(Element) * 8) {
             if (srcElem1 != 0) {
-                destElem = (Element)1 << (sizeof(Element) * 8 - 1);
+                destElem = std::numeric_limits<Element>::min();
                 if (srcElem1 > 0)
                     destElem = ~destElem;
                 fpscr.qc = 1;
@@ -2986,7 +2990,7 @@ let {{
                                     sizeof(Element) * 8 - 1,
                                     sizeof(Element) * 8 - 1 - imm);
             if (topBits != 0 && topBits != mask(imm + 1)) {
-                destElem = (Element)1 << (sizeof(Element) * 8 - 1);
+                destElem = std::numeric_limits<Element>::min();
                 if (srcElem1 > 0)
                     destElem = ~destElem;
                 fpscr.qc = 1;
@@ -3489,7 +3493,7 @@ let {{
 
     vqabsCode = '''
         FPSCR fpscr = (FPSCR) FpscrQc;
-        if (srcElem1 == (Element)((Element)1 << (sizeof(Element) * 8 - 1))) {
+        if (srcElem1 == (Element)(std::numeric_limits<Element>::min())) {
             fpscr.qc = 1;
             destElem = ~srcElem1;
         } else if (srcElem1 < 0) {
@@ -3504,7 +3508,7 @@ let {{
 
     vqnegCode = '''
         FPSCR fpscr = (FPSCR) FpscrQc;
-        if (srcElem1 == (Element)((Element)1 << (sizeof(Element) * 8 - 1))) {
+        if (srcElem1 == (Element)(std::numeric_limits<Element>::min())) {
             fpscr.qc = 1;
             destElem = ~srcElem1;
         } else {