Dead stores in src/common/sha2.c

[Hamlin, Garick L]

I ran clang checker and noticed these.   It looks like the 
sha2 implementation is trying to zero out state on exit, but
clang checker finds at least 'a' is a dead store.  

Should we fix this?
Is something like the attached sensible?
Is there a common/better approach to zero-out in PG ?

Garick

diff --git a/src/common/sha2.c b/src/common/sha2.c
index ae0a1a3..9c19ef2 100644
--- a/src/common/sha2.c
+++ b/src/common/sha2.c
@@ -457,7 +457,16 @@ SHA256_Transform(pg_sha256_ctx *context, const uint8 *data)
        context->state[7] += h;
 
        /* Clean up */
-       a = b = c = d = e = f = g = h = T1 = T2 = 0;
+       *((volatile uint32 *) &a) = 0;
+       *((volatile uint32 *) &b) = 0;
+       *((volatile uint32 *) &c) = 0;
+       *((volatile uint32 *) &d) = 0;
+       *((volatile uint32 *) &e) = 0;
+       *((volatile uint32 *) &f) = 0;
+       *((volatile uint32 *) &g) = 0;
+       *((volatile uint32 *) &h) = 0;
+       *((volatile uint32 *) &T1) = 0;
+       *((volatile uint32 *) &T2) = 0;
 }
 #endif                                                 /* 
SHA2_UNROLL_TRANSFORM */
 
@@ -693,7 +702,15 @@ SHA512_Transform(pg_sha512_ctx *context, const uint8 *data)
        context->state[7] += h;
 
        /* Clean up */
-       a = b = c = d = e = f = g = h = T1 = 0;
+       *((volatile uint32 *) &a) = 0;
+       *((volatile uint32 *) &b) = 0;
+       *((volatile uint32 *) &c) = 0;
+       *((volatile uint32 *) &d) = 0;
+       *((volatile uint32 *) &e) = 0;
+       *((volatile uint32 *) &f) = 0;
+       *((volatile uint32 *) &g) = 0;
+       *((volatile uint32 *) &h) = 0;
+       *((volatile uint32 *) &T1) = 0;
 }
 #else                                                  /* 
SHA2_UNROLL_TRANSFORM */
 
@@ -783,7 +800,16 @@ SHA512_Transform(pg_sha512_ctx *context, const uint8 *data)
        context->state[7] += h;
 
        /* Clean up */
-       a = b = c = d = e = f = g = h = T1 = T2 = 0;
+       *((volatile uint32 *) &a) = 0;
+       *((volatile uint32 *) &b) = 0;
+       *((volatile uint32 *) &c) = 0;
+       *((volatile uint32 *) &d) = 0;
+       *((volatile uint32 *) &e) = 0;
+       *((volatile uint32 *) &f) = 0;
+       *((volatile uint32 *) &g) = 0;
+       *((volatile uint32 *) &h) = 0;
+       *((volatile uint32 *) &T1) = 0;
+       *((volatile uint32 *) &T2) = 0;
 }
 #endif                                                 /* 
SHA2_UNROLL_TRANSFORM */